T  E 

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GIFT  OF 


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Published     by 

HE  ATLAS  PORTLAND  CEMENT  CO 

30  Broad  St..  N  Y. 


CONCRETE  IN 

HIGHWAY 
CONSTRUCTION 


A  Text-Book  for   Highway 
Engineers  and  Supervisors 


Price  $1.00 


Published     by 

THE   ATLAS   PORTLAND   CEMENT   CO. 

30    Broad    Street 

NEW  YORK 


\ 


A1 


Copyright,  1909 

by 

THE  ATLAS  PORTLAND  CEMENT  Co. 
30  Broad  Street,  N.  Y. 

SECOND  EDITION 
All  rights  reserved 


254070 


•••„ '  5*  *•••*•"     * 


INDEX. 

PAGE 

Foreword   9 

CHAPTER  I. — CONCRETE. 

Cement 13 

Storing  Cement 14 

Sand  or  Fine  Aggregate 14 

Coarse  Aggregate 15 

Water 16 

Proportions  of  Materials 16 

Quantities  of  Materials  in  Concrete 18 

Table  of  Volume  of  Concrete  Made  from  One  Barrel  of  Portland  Cement.  .  18 

Table  of  Quantities  of  Material  per  Cubic  Yard  of  Rammed  Concrete 19 

Table  of  .Volume  of  Plastic   Mortar  Made   from  Different   Proportions  of 

Cement  and  Sand 20 

Rubble   Concrete 20 

Mixing  Concrete 20 

Hand   Mixing 21 

Placing   Concrete 23 

Laying  Concrete  in  Water 23 

Laying  Concrete  in  Sea  Water 24 

Effect  of  Manure 24 

Freezing 24 

Forms  25 

CHAPTER  II. — SIDEWALKS,  CURBS  AND  GUTTERS. 

Dimensions  of  Walks,  Curbs  and  Gutters 27 

Foundations  and  Drainage 28 

Proportions  for  Concrete 30 

Forms 30 

Placing   Concrete. 31 

Coloring  Matter 35 

Table  of  Materials  for  Concrete  Sidewalks,  Floors  and  Walls 35 

Quantities   of   Material 36 

Cost 36 

Vault  Light  Construction 38 

CHAPTER  III. — STREET  PAVEMENTS. 

Concrete  Street  Pavement  Foundations 41 

Proportions  of  Concrete  for  Street  Foundations.  .  42 


PAGE 

Cost  of  Concrete  Foundations  in  Place 42 

Mixing  of  Concrete 43 

Gang  for  Hand-Mixed  Concrete 43 

Construction  of  Foundations 44 

Crowning  of  Roadways 44 

Table  of  Offsets  for  Crowning  Streets  of  Various  Widths 45 

Foundations  Under  Street  Railway  Tracks 46 

Concrete   Pavements    46 

Essentials  of  a  Concrete  Pavement 47 

Blome  Company  Granitoid  Concrete  Pavement 48 

General  Specifications  for  the  Blome  Company  Granitoid  Concrete  Blocked 

Pavement , 49 

Preparation  of  Sub-Grade 49 

Foundation    49 

Materials    49 

Sand    49 

Crushed    Stone . 50 

"Gravel    50 

Mixing  and  Laying  of  Concrete  and  Formation  of  the  Blome  Company  Grani- 
toid  Blocking    50 

Surfacing   Material '. 50 

Expansion   Joints 51 

Patents 51 

Guaranty    51 

Bidders'  Attention 51 

Cost  of  Blome  Company  Granitoid  Pavement 52 

Hassani  Pavement 53 

Hassam  Grouted  Concrete  Pavement 53 

Long  Island  Motor  Parkway 54 

Cost  of  Hassani  Pavement 56 

Hassani  Granite  Block  Pavement 56 

Concrete  Pavement  in  Richmond,  Ind 57 

Concrete  Pavements  in  the  City  of  Panama 58 

Grouting  Stone  Block  and  Brick  Pavements 59 

CHAPTER  IV.— SEWERS,  DRAIN  TILES,  BROOK  LININGS  AND  CONDUITS. 

Sewers 60 

Concrete  Pipe  Sewers 61 

Table  of  Tests  of  Plain  Concrete  Sewer  Pipe  in  Brooklyn. 61 


PAGE 

Large  Concrete  Sewers 63 

Table  of  Thickness  of  Conduits 63 

Sizes  of  Circular  Concrete  Sewer  Pipe 63 

Proportions  of  Concrete  for  Sewer  Pipe 64 

Concrete  Drain  Tile 65 

Size  of  Concrete  Drain  Tiles 65 

Mixtures  for  Tiles 65 

Curing    65 

Laying  Drain  Tiles 66 

Brook   Linings 67 

Conduits  69 

CHAPTER  V. — CULVERTS. 

Box  Culverts 73 

Circular  or  Pipe  Culverts 78 

Arch  Culverts 79 

Table  of  Quantity  of  Materials  for  Arch  Culverts 84 

Preparing   the   Bed 84 

Forms  for  Arch  Culverts 85 

CHAPTER  VI. — BEAM  BRIDGES. 

Kinds  of  Concrete  Bridges 88 

Types  of  Flat  Bridges 88 

Proportions  for  Concrete 89 

Steel    Reinforcement 89 

Slab  Bridges 89 

Table  of  Principal  Dimensions  and  Quantities  of  Materials  for  Slab  Bridges.  91 

Combination  Beam  and  Slab  Bridges 93 

Method  of  Construction  of  Combined  Beam  and  Slab  Bridges 97 

Girder  Bridges 97 

Concrete  Floors  for  Steel  Bridges 99 

Cost  of  Beam  and  Slab  Bridges 100 

CHAPTER  VII. — ARCH  BRIDGES. 

Plain  and  Reinforced  Concrete  Arches 102 

History  of  Concrete  Arches 103 

Types  of  Concrete  Arches 103 

Preparation  of   Plans 104 

Design  for  Forty-Foot  Span 105 


PAGE 

Expansion   Joints 107 

Reinforced  Concrete  Arch,  Elm  Street,  Concord,  Mass 107 

Falsework  and  Centering Ill 

Placing   Concrete Ill 

Earth    Filling 114 

Striking    Centers 114 

Surface    Finishing 114 

Cost    115 

CHAPTER  VII. — RETAINING  WALLS. 

Kinds  of  Retaining  Walls 118 

Gravity   Retaining  Walls 120 

Copings    121 

Forms  for  Gravity  Walls 122 

Dimensions  of  Gravity  Walls 123 

Table  of  Dimensions  and  Quantities  of  Gravity  Retaining  Walls 123 

Reinforced  Retaining  Walls 124 

Proportions  of  Concrete 126 

Expansion   Joints 127 

Drainage    127 

CHAPTER  IX. — MISCELLANEOUS. 

Fence    Posts 128 

Concrete  Fence  Posts  at  Dellwood  Park 130 

Hitching  Posts 131 

Lamp    Posts 132 

Drinking  Fountains 133 


FOREWORD. 

The  development  of  manufacture  and  of  agriculture,  which  require  proper 
transportation  facilities  not  only  on  the  railroads  but  to  the  points  of  ship- 
ment and  distribution,  has  stimulated  a  widespread  interest  and  called  national 
attention  to  the  necessity  for  better  pavements  and  for  highway  constructions 
of  a  more  permanent  and  durable  character. 

This  demand,  as  well  as  the  necessity  for  reducing  the  expense  of  repairs 
incident  to  automobile  traffic,  has  brought  to  the  forefront  the  use  of  concrete 
to  produce  permanent  construction,  not  only  for  sidewalks  and  pavements,  but 
for  highway  structures,  such  as  bridges,  retaining  walls,  culverts,  and  the 
many  smaller  details,  the  repairs  to  which  are  continually  vexing  the  City 
and  Town  Engineer  and  the  Highway  Commissioner. 

The  purpose  of  the  present  volume,  then,  is  to  present  to  those  in  charge  of 
street  and  highway  construction  and  maintenance,  examples  of  work  which 
have  been  satisfactorily  performed,  and,  further,  to  give  drawings  and  designs 
made  especially  for  The  "ATLAS"  Portland  Cement  Company,  either  as 
reproductions  of  existing  structures,  from  drawings  and  photographs  kindly 
furnished  by  the  local  authorities,  or  as  original  designs  prepared  by  expert 
engineers  at  the  request  of  the  "ATLAS"  Portland  Cement  Company. 

The  most  important  matter  of  sidewalk  construction  is  taken  up  in  con- 
siderable detail,  while  concrete  street  pavement  construction  has  been  thor- 
oughly investigated,  and  recommendations  made  of  methods  which  have 
produced  durable  and  satisfactory  results.  Numerous  examples  and  sugges- 
tions are  given  in  the  line  of  bridge  design  and  construction,  both  for  arches 
and  flat  bridges;  sewers,  culverts  and  retaining  walls  are  quite  thoroughly 
treated;  and  such  minor  structures  as  drains,  brook  linings,  fences  and  posts, 
are  illustrated  and  described. 


Although  the  information  in  this  little  volume  is  more  valuable  and  in 
much  greater  detail  than  is  customarily  presented  by  manufacturing  com- 
panies, the  position  of  The  "ATLAS"  Portland  Cement  Company  as  the  lead- 
ing cement  manufacturers  in  the  world  has  led  them  to  present  data  which  will 
tend  not  only  toward  an  increasing  use  of  cement  but  toward  a  use  of  cement 
according  to  the  best,  safest  and  most  economical  practice. 

This  present  volume  together  with  the  other  books  of  The  "ATLAS" 
Portland  Cement  Company,  namely,  "Concrete  Construction  About  the  Home 
and  on  the  Farm" ;  "Concrete  Country  Residences" ;  "Reinforced  Concrete  in 
Factory  Construction,"  and  "Concrete  in  Railroad  Construction,"  covers  a 
wide  range  in  the  use  of  concrete, 

THE  ATLAS  PORTLAND  CEMENT  COMPANY. 
New  York,  June,  1909. 


10 


CHAPTER  I. 
CONCRETE. 

During  the  year  1907  the  State  Highway  Commission  of  Massachusetts 
spent  $468,000  in  the  construction  of  new  roads  and  $106,000  for  repairs  and 
maintenance  of  roads  in  its  charge.  The  State  Highway  Department  of  Penn- 
sylvania expended  $3,187,000  in  the  construction  of  new  roads  up  to  January 
i,  1908,  and  in  the  report  of  this  department  for  1907  the  sum  of  $29,225,000 
is  given  as  the  total  cost  of  roads  completed,  under  contract  and  to  be  built. 
Other  States  are  similarly  engaged  in  building  new  roads,  and  improving  old 
ones  so  that  the  movement  for  better  roads  and  streets  is  almost  universal. 
Such  enormous  costs  of  construction  and  maintenance  show  the  necessity  for 
the  selection  of  materials  which,  in  the  long  run,  are  the  cheapest  and  most 
economical. 

Concrete  is  playing  a  large  part  in  this  construction  and  re-construction, 
not  so  much  in  the  roadbed  proper,  although  as  is  shown  in  the  pages  which 
follow,  concrete  street  pavements  are  well  adapted  to  certain  conditions,  but 
especially  for  the  various  structures  which  are  necessarily  incidental  to  road 
building. 

This  class  of  work  includes  not  only  such  structures  as  are  necessary  in 
first-class  streets  or  highways,  such  as  culverts,  bridges  and  retaining  walls, 
but  also  in  the  roadway  itself,  either  as  a  foundation  for  a  stone,  brick  or 
asphalt  surface,  or  as  a  complete  pavement  including  foundations  and  wearing 
surfaces. 

For  smaller  uses  concrete  has  a  still  wider  field.  For  sidewalks,  curbs  and 
gutters  its  use  is  becoming  quite  universal,  while  as  a  material  for  drain  tiles, 
lamp  posts  of  various  styles,  hitching  posts,  fence  posts,  and  many  other 
highway  appurtenances,  its  value  is  fast  being  recognized,  as  is  shown  by  the 
enormous  increase  in  its  use  for  such  purposes.  As  a  material  for  building 
park  structures,  such  as  bridges,  buildings,  drinking  fountains,  and  seats,  con- 
crete is  well  suited  because  of  its  cheapness,  durability,  and  the  ease  with 
which  it  is  molded  into  artistic  designs. 

In  the  larger  structures  such  as  bridges  and  retaining  walls,  especially 
where  steel  reinforcement  is  necessary  to  give  the  required  strength,  a  proper 
design  with  good  working  drawings  showing  the  dimensions  and  the  location 
of  the  steel  is  of  the  utmost  importance,  and  where  the  structure  is  of  appre- 

ii 


ciable  size  a  competent  engineer  familiar  with  the  principles  of  design  and 
with  practical  construction  in  concrete  should  be  employed  to  prepare  plans 
and  specifications,  and  to  superintend  the  construction.  On  the  other  hand, 
many  of  the  minor  details  can  be  built  with  but  little  engineering  experience, 
provided  directions  given  by  competent  authorities  are  carefully  followed, 
and  good  judgment  is  used  in  the  selection  of  the  materials  and  in  the  work 
of  construction. 

The  principal  requisites  of  a  material  used  in  building  various  structures 
forming  the  necessary  parts  of  a  well-constructed,  modern  highway  are  cheap- 
ness and  durability.  If  the  first  cost  of  the  structure  is  to  be  small  the  mate- 
rials used  in  its  construction  must  be  cheap  and  must  be  easily  placed  in  posi- 
tion by  ordinary  workmen,  and  if  the  cost  of  maintenance  is  not  to  be  excess- 
ive the  materials  used  must  possess  qualities  that  will  enable  them  to  with- 
stand the  elements  successfully.  Wood,  steel,  stone,  and  concrete  are  in 
general  the  principal  materials  used  in  the  construction  of  highway  appur- 
tenances such  as  bridges,  culverts,  sidewalks,  curbs,  and  gutters.  Of  these 
four  materials  wood  is  usually  the  cheapest  in  first  cost  for  small  structures 
and  is  the  least  durable  of  all.  The  cost  of  maintenance  of  ordinary  wooden 
bridges  is  so  great  and  the  life  is  so  short  that  wood  is  really  no  longer  con- 
sidered seriously  as  a  material  for  first-class  construction,  especially  in  those 
localities  where  lumber  is  scarce.  Stone  is  generally  a  durable  material  of 
construction,  but  its  first  cost,  and  in  many  places  its  scarcity,  tend  to  limit 
its  use  for  highway  purposes.  It  is  also  difficult  and  expensive  to  shape  stone 
into  desired  forms  which  in  many  cases  are  required  to  secure  the  best  re- 
sults. The  importance  of  steel  in  the  construction  of  highway  bridges  of  long 
spans  is  well  understood,  but  its  cost  and  the  constant  heavy  maintenance 
charges,  or  its  rapid  deterioration  if  not  properly  maintained,  have  caused 
builders  of  bridges  to  seek  some  other  material  which  is  lower  in  first  cost  and 
which  will  not  require  constant  painting.  Clearly,  concrete,  or  concrete  with 
steel  imbedded  in  it  to  reinforce  it,  is  the  material  above  all  others  that  com- 
bines the  advantages  of  cheapness  and  durability.  Concrete  can  be  made  at 
small  expense  in  practically  any  locality;  can  be  molded  in  any  desired  shape 
or  size;  requires  no  maintenance,  and  can  be  placed  in  position  with  very 
little  skilled  labor. 

In  making  concrete  the  cement,  sand,  and  stone  or  gravel  should  be  care- 
fully chosen,  thoroughly  mixed,  and  properly  laid.  If  these  precautions  are 
taken  the  mass  will  begin  to  stiffen  in  an  hour  or  so  after  being  laid  and  will 
continue  to  harden  until  in  about  one  month's  time  the  mass  becomes  a  hard 
compact  stone. 


12 


CEMENT. 

Portland  cement  of  first-class  reputation  should  be  used  to  obtain  the 
greatest  uniformity,  reliability  and  the  highest  strength.  If  the  work  is  small 
and  unimportant  and  a  brand  of  cement  of  first-class  reputation  is  purchased 
from  a  reliable  dealer  no  testing  is  necessary,  but  for  important  structures  the 
cement  should  be  tested  and  should  meet  the  requirements  of  the  American 
Society  for  Testing  Materials.*  If  it  is  impracticable  to  make  these  complete 
tests,  specimens  may  be  made  to  see  if  the  cement  sets  up  properly.  The 
following,  also,  is  a  simple  test  for  determining  the  soundness  of  the  cement : 

A  sound  cement  will  not  crumble  when  placed  in  the  work  and  a  test  for 
soundness  is  therefore  of  considerable  importance.  Oftentimes  no  other  test 
need  be  made.  Mix,  by  kneading  i*^  minutes,  one  cupful  of  Portland 
cement  with  enough  water  to  form  a  paste  having  a  consistency  like  that 
of  ordinary  putty.  Place  part  of  this  paste  on  each  of  3  pieces  of  glass  about 
4  inches  square  so  as  to  make  a  pat  about  3  inches  in  diameter  and  ^  inch 
thick  at  the  center  tapering  down  to  a  thin  edge.  Leave  these  3  pats  under 
a  damp  cloth  arranged  so  that  it  will  not  touch  them  for  24  hours.  Then 
place  one  pat  in  air  at  an  ordinary  temperature  for  28  days,  a  second  pat  in 
water  for  28  days,  and  the  third  pat  in  a  tightly  closed  vessel  over  boiling 
water  for  5  hours.  If  the  cement  is  of  good  quality  the  pats  will  show  no 
radial  cracks  and  they  will  not  crumble.  If  the  time  is  limited  and  the  pat 
placed  in  steam  shows  no  signs  of  crumbling  the  cement  may  be  accepted 
on  this  steam  test  alone. 

Portland  cement  is  manufactured  from  a  mixture  of  two  materials,  one  of 
them  a  rock  like  limestone  or  a  softer  material  like  chalk  which  is  nearly  pure 
dime,  and  another  material  like  shale,  which  is  a  hardened  clay,  or  else  clay 
itself.  In  other  words,  there  must  be  one  material  which  is  largely  lime  and 
another  material  which  is  largely  clay,  and  these  two  must  be  mixed  in  very 
exact  proportions  determined  by  chemical  tests,  the  proportions  of  the  two 
being  changed  every  few  hours  to  allow  for  the  variation  in  the  chemical  com- 
position of  the  materials. 

"ATLAS"  Portland  Cement  is  made  by  quarrying  each  of  these  materials, 
crushing  them  separately,  mixing  them  in  the  exact  proportions,  and  grinding 
them  to  a  very  fine  powder.  This  powder  is  fed  into  long  rotary  kilns,  which 
are  iron  tubes  about  5  or  6  feet  in  diameter  lined  with  fire  brick  and  over  100 
feet  long.  Powdered  coal  is  also  fed  into  the  kilns  and  burned  at  a  tempera- 
ture of  about  3,000  deg.  Fahr.,  a  temperature  higher  than  that  needed  to  melt 
iron  to  a  liquid  and  there  is  formed  what  is  called  cement  clinker,  a  kind  of 
dark  porous  stone  which  looks  almost  exactly  like  lava. 


These  may  be  obtained  by  addressing  The  Atlas  Portland  Cement  Company. 

13 


After  leaving  the  kiln,  the  clinker  is  cooled,  crushed,  and  ground  again  to  a 
still  finer  powder,  so  fine,  in  fact,  that  most  of  the  particles  are  less  than  1/200 
of  an  inch  in  size,  and  this  grinding  produces  the  light  gray-colored  powder 
characteristic  of  "ATLAS"  Portland  Cement. 

It  is  now  placed  in,  storage  tanks  or  stock  houses  where  it  should  remain 
for  a  while  to  season  before  it  is  put  into  bags  or  barrels  and  shipped.  The 
barrels  weigh  400  pounds  gross,  or  376  pounds  net.  When  shipped  in  bags 
the  weight  is  94  pounds  per  bag,  four  bags  being  equal  to  one  barrel. 

At  the  "ATLAS"  plants  from  the  time  the  rock  is  taken  from  the  quarry 
until  it  is  packed  in  barrels  or  bags  all  of  the  work  is  done  by  machinery,  and 
a  thorough  chemical  mixture  takes  place  regulated  by  the  experienced  chem- 
ists in  charge  of  the  work. 

STORING  CEMENT. 

Cement  should  come  packed  in  barrels  or  in  stout  cloth  or  canvas  bags  and 
should  be  stored  in  a  dry  place,  preferably  a  house  or  shed  until  used,  or  if  no 
such  storage  house  is  available  the  cement  should  be  placed  on  a  wooden  plat- 
form raised  at  least  6  inches  above  the  ground  and  should  be  covered  so  as  to 
exclude  water.  When  used  the  cement  should  be  free  from  lumps. 

SAND   OR  FINE  AGGREGATE. 

The  term  aggregate  includes  the  stone  and  sand  in  concrete  and  may  be 
classified  as  fine  and  coarse.  The  fine  aggregate  may  be  sand  or  crushed  stone 
or  gravel  screenings  which  will  pass  when  dry  a  screen  having  *4  incn  diam- 
eter holes.  If  sand  is  used  it  should  be  clean  and  coarse,  or  a  mixture  of  coarse 
and  fine  grains  with  the  coarse  grains  predominating.  It  should  be  free  from 
loam,  clay,  mica,  sticks,  fine  roots,  or  other  impurities.  Sand  should  be  coarse, 
that  is,  it  should  have  a  considerable  portion  of  its  grains  measuring  1/32  to 
%  inch  in  diameter  and  should  the  grains  run  up  to  J4  inch  the  strength  of  the 
mortar  is  increased. 

Vegetable  loam  is  frequently  very  injurious  to  concrete  and  great  care 
should  be  taken  in  selecting  and  excavating  to  see  that  the  sand  does  not  con- 
tain any  vegetable  matter.  For  all  important  structures  the  sand  should  be 
tested  in  a  laboratory  as  described  in  the  following  paragraphs : 

"Mortars  composed  of  one  part  Portland  cement  and  three  parts  fine  aggre- 
gate by  weight  when  made  into  briquets  should  show  a  tensile  strength  of  at 
least  70  per  cent  of  the  strength  of  1 13  mortar  of  the  same  consistency  made 
with  the  same  cement  and  standard  Ottawa  sand.  To  avoid  the  removal  of 
any  coating  on  the  grains  which  may  affect  the  strength,  bank  sands  should 
not  be  dried  before  being  made  into  mortar  but  should  contain  natural  mois- 

14 


ture.  The  percentage  of  moisture  may  be  determined  upon  a  separate  sample 
for  correcting  weight  of  the  sand.  From  10  to  40  per  cent  more  water  may  be 
required  in  mixing  bank  or  artificial  sands  than  for  standard  Ottawa  sand  to 
produce  the  same  consistency."* 

"The  relative  strength  of  mortars  from  different  sands  is  largely  affected  by 
the  size  of  the  grains.  A  coarse  sand  gives  a  stronger  mortar  than  a  fine  one, 
and  generally  a  gradation  of  grains  from  fine  to  coarse  is  advantageous.  If  a 
sand  is  so  fine  that  more  than  10  per  cent  of  the  total  dry  weight  passes  a  No. 
100  sieve,  that  is,  a  sieve  having  100  meshes  to  the  linear  inch,  or  if  more  than 
35  per  cent  of  the  total  dry  weight  passes  a  sieve  having  50  meshes  per  linear 
inch,  it  should  be  rejected  or  used  with  a  large  excess  of  cement."* 

Crushed  stone  or  gravel  screenings,  when  used  in  place  of  sand,  should  pass 
when  dry  a  screen  having  J4-inch  diameter  holes  or  a  screen  having  4  meshes 
to  the  linear  inch  and  if  free  from  impurities  may  be  substituted  for  a  part  or 
the  whole  of  the  sand  in  such  proportions  as  to  give  a  dense  mixture. 

COARSE  AGGREGATE 

Gravel  or  crushed  stone  of  a  hard  and  durable  quality  make  up  the  coarse 
aggregate  for  concrete.  The  best  materials  are  trap  rock,  hard  limestone, 
granite,  or  conglomerate  of  size  retained  on  a  screen  having  %-inch  diameter 
holes. 

Aggregates  containing  soft,  flat,  or  elongated  particles  should  be  excluded 
from  important  structures.  Stone  which  breaks  into  cubical  or  similar  angu- 
lar forms  is  much  preferable  in  any  case  to  that  which  breaks  into  flat  layers 
because  it  gives  a  stronger  concrete  and  one  which  is  more  readily  placed. 
Graded  sizes  of  particles,  that  is,  particles  varying  from  small  to  large  sizes,  are 
generally  advantageous.  Where  concrete  is  used  in  mass,  the  crushed  stone  or 
gravel  may  range  in  size  from  %  inch  to  that  which  passes  through  a  3-inch 
ring.  For  reinforced  concrete,  the  particles  must  be  small  enough  to  flow  into 
place  around  and  between  the  steel  bars  and  into  all  corners  of  the  forms.  For 
this  a  maximum  size  of  i  inch  (that  is,  the  largest  particle  small  enough  to  go 
through  a  i-inch  ring),  or  in  other  cases  a  ^-inch  or  %-inch  must  be  used. 
The  material  passing  the  ^4-inch  screen  may  be  used  as  a  part  of  the  sand. 

If  gravel  is  used  instead  of  crushed  stone,  it  should  be  of  a  size  to  be  easily 
handled  and  easily  placed  around  the  steel  if  there  is  steel  reinforcement  and 
it  should  be  clean  and  free  from  vegetable  or  other  deleterious  matter.  As  in 
the  case  of  crushed  stone,  the  material  below  *4  incn  m  slze  should  be  screened 
out  to  be  used  as  sand.  Sand  and  gravel  are  rarely  found  mixed  in  the  proper 


*Report    of    Committee    on    Reinforced    Concrete,    1909,    National    Association    of 
Cement  Users. 

15 


proportions  in  the  natural  bank,  and  it  is  cheaper  to  screen  and  remix  them  in 
the  correct  proportions  than  to  use  the  richer  mixture  necessary  with  un- 
screened material. 

Pebbles  of  graded  sizes  with  the  larger  sizes  predominating  are  preferable 
to  pebbles  of  a  uniform  size  because  they  are  more  readily  mixed  and  placed. 

For  important  structures  and  for  structures  where  there  will  be  considerable 
wear  on  the  concrete,  the  materials  should  be  carefully  selected,  but  for  unim- 
portant structures  it  is  usually  sufficient  to  make  two  small  blocks  of  concrete, 
say  6-inch  cubes,  and  place  one  of  these  cubes  out-of-doors  in  air  for  7  days 
and  the  other  in  a  fairly  warm  room. 

The  specimen  placed  in  the  warm  room  should  be  hard  enough  at  the  end 
of  24  hours  to  bear  pressure  from  the  thumb  without  indentation  and  it  also 
should  whiten  out  to  some  extent  during  this  time.  The  specimen  placed  out- 
of-doors  should  be  hard  enough  to  remove  from  the  mold  at  the  end  of  24 
hours  in  ordinary  mild  weather  or  48  hours  in  cold  damp  weather.  At  the  end 
of  a  week  test  both  blocks  by  hitting  them  with  a  hammer.  If  the  hammer 
does  not  dent  them  under  light  blows  such  as  would  be  used  in  driving  tacks 
and  the  blocks  sound  hard  and  are  not  broken  under  these  blows  the  sand  as  a 
general  rule  can  be  used. 

WATER. 

Water  used  in  mixing  concrete  should  be  free  from  oil,  acids,  alkalies,  or 
vegetable  matter. 

PROPORTIONS  OF  MATERIALS. 

The  following  paragraphs  relating  to  the  proper  proportions  of  materials 
for  making  concrete  are  taken  from  "Concrete  Construction  About  the  Home 
and  on  the  Farm" :  * 

"Concrete  is  composed  of  a  certain  amount  or  proportion  of  cement,  a  larger 
amount  of  sand,  and  a  still  larger  amount  of  stone.  The  fixing  of  the  quanti- 
ties of  each  of  these  materials  is  called  proportioning.  The  proportions  for  a 
mix  of  concrete  if  given,  for  instance,  as  one  part  of  cement  to  two  parts  of 
sand  to  four  parts  of  stone  or  gravel,  are  written  1 12 14,  and  this  means  that 
one  cubic  foot  of  packed  cement  is  to  be  mixed  with  two  cubic  feet  of  sand  and 
with  four  cubic  feet  of  loose  stone. 

"For  ordinary  work,  use  twice  as  much  coarse  aggregate  (that  is,  gravel  or 
stone)  as  fine  aggregate  (that  is,  sand). 

"If  gravel  from  a  natural  bank  is  used  without  screening,  use  the  same  pro- 
portions called  for  of  the  coarse  aggregate;  that  is,  if  the  specifications  call  for 
proportions  of  1 12 14,  as  given  above,  use  for  unscreened  gravel  (provided  it 


*Published  by  The  Atlas  Portland  Cement  Company,  from  whom  it  can  be   ob- 
tained by  making  application  for  same. 

16 


contains  quite  a  large  quantity  of  stone)  one  part  cement  to  four  parts  un- 
screened gravel. 

"If  when  placing  concrete  with  the  proportions  specified,  a  wall  shows 
many  voids  or  pockets  of  stone,  use  a  little  more  sand  and  a  little  less  stone 
than  called  for.  If  on  the  other  hand,  when  placing,  a  lot  of  mortar  rises  to  the 
top,  use  less  sand  and  more  stone  for  the  next  batch. 

"In  calculating  the  amount  of  each  of  the  materials  to  use  for  any  piece  of 
work,  do  not  make  the  mistake  so  often  made  by  the  inexperienced  that  one 
barrel  of  cement,  two  barrels  of  sand,  and  four  barrels  of  stone,  will  make 
seven  barrels  of  concrete.  As  previously  stated,  the  sand  fills  in  the  voids  be- 
tween the  stones,  while  the  cement  fills  the  voids  between  the  grains  of  sand, 
and  therefore  the  total  quantity  of  concrete  will  be  slightly  in  excess  of  the 
original  quantity  of  stone." 

The  unit  of  measure  is  the  barrel,  which  should  be  taken  as  containing  3.8 
cubic  feet.  Four  bags  containing  94  pounds  of  cement  each  are  equivalent  to 
one  barrel.  Sand  and  stone  or  gravel  should  be  measured  separately  as  loosely 
thrown  into  the  measuring  receptacle. 

The  following  quotation  from  "Concrete,  Plain  and  Reinforced"*  by  the 
well-known  authorities,  Taylor  and  Thompson,  is  printed  as  a  guide  to  those 
who  wish  to  build  any  concrete  structure  for  which  specific  instructions  are 
not  given  in  the  following  pages : 

"As  a  rough  guide  to  the  selection  of  materials  for  various  classes  of  work, 
we  may  take  four  proportions  which  differ  from  each  other  simply  in  the  rela- 
tive quantity  of  cement" : 

(a)  A  Rich  Mixture  for  columns  and  other  structural  parts  subjected  to  high 
stresses  or  requiring  exceptional  water  tightness:      Proportions — 1:1^:3;  that  is, 
one  barrel  (4  bags)  packed  Portland  cement  to  T.y2  barrels  (5.7  cubic  feet)  loose 
sand  to  3  barrels  (11.4  cubic  feet)  loose  gravel  or  broken  stone. 

(b)  A  Standard  Mixture  for  reinforced  floors,  beams  and  columns,  for  rein- 
forced engine   or   machine  foundations   subject   to   vibrations,   for   tanks,   sewers, 
conduits,  and  other  water-tight   work:     Proportions — 1:2:4;   that  is,   one  barrel 
(4  bags)  packed  Portland  cement  to  2  barrels   (7.6  cubic  feet)   loose  sand  to  4 
barrels  (15.2  cubic  feet)  loose  gravel  or  broken  stone. 

(c)  A  Medium  Mixture  for  ordinary  machine  foundations,  retaining  walls,  abut- 
ments, piers,  thin  foundation  walls,  building  walls,  ordinary  floors,  sidewalks,  and 
sewers   with  heavy  walls:  Proportions — 1:2^:5;    that    is,    one    barrel    (4    bags) 
packed  Portland  cement  to  2l/2  barrels  (9.5   cubic   feet)    loose   sand  to   5   barrels 
(19  cubic  feet)  loose  gravel  or  broken  stone. 

(d)  A  Lean  Mixture  for  unimportant  work  in  masses,  for  heavy  walls,  for  large 
foundations   supporting  a  stationary  load,   and  for   backing   for  stone  masonry: 
Proportions — 1:3:6;   that  is,   one  barrel   (4  bags)   packed  Portland  cement  to  3 
barrels  (11.4  cubic  feet)  loose  sand  to  6  barrels  (22.8  cubic  feet)  loose  gravel  pr 
broken  stone. 

*See  reference,  footnote,  page  18. 

17 


QUANTITIES  OF  MATERIALS  IN  CONCRETE. 

In  estimating  the  quantities  of  cement,  sand,  and  broken  stone  or  gravel  in 
a  given  volume  of  concrete  or  in  estimating  the  volume  of  mortar  or  concrete 
which  can  be  made  from  one  barrel  of  cement  the  three  accompanying  tables 
will  be  found  useful.  The  values  given  in  the  tables  are  computed  from  results 
of  actual  experiments  and  have  been  checked  with  concrete  laid  in  large  masses. 


VOLUME  OF  CONCRETE  MADE  FROM  ONE  BARREL  OF  PORTLAND  CEMENT* 
Based  on  a  Barrel  of  3.8  Cubic  Feet 


Volume  of 

Average  Volume  of  Rammed 
Concrete  Made  From  One 

Proportions 

Proportions 

Mortar  in 

Barrel  of  Cement 

by  Parts 

by  Volume 

Terms  of 

Percentage 
of  Volume 
of 

Percentages   of  Voids   in 
Broken  Stone  or  Gravel 

Cem't 

Sand 

Stone 

Cem't 

Sand 

Stone 

Stone 

60%t 

45%t 

40%§ 

bbl. 

cu.  ft. 

cu.  ft. 

per  cent. 

cu.  ft. 

cu.  ft. 

cu.  ft. 

1 

1 

2 

1 

3.8 

7.6 

75 

9.5 

9.9 

10.3 

1 

1 

3 

1 

3.8 

11.4 

51 

11.5 

12.2 

12.8 

1 

1H 

3 

1 

6.7 

11.4 

64 

12.9 

13.5 

14.1 

1 

1H 

3^ 

1 

5.7 

13.3 

55 

13.9 

14.6 

15.4 

1 

2 

3 

1 

7.6 

11.4 

75 

14.3 

14.9 

15.5 

1 

2 

4 

1 

7.6 

15.2 

57 

16.3 

17.2 

18.0 

1 

2^ 

4^ 

1 

9.5 

17.1 

60 

18.7 

19.6 

20.6 

1 

2^ 

5 

1 

9.5 

19.0 

54 

19.8 

20.8 

21.8 

1 

3 

5 

1 

11.4 

19.0 

61 

211 

22.1 

23.2 

1 

3 

6 

1 

11.4 

22.8 

52 

23.2 

24.4 

25.6 

Note. — Variations  in  the  fineness  of  the  sand  and  the  compacting  of  the  concrete  may  affect  the  volumes  by 
10%  in  either  direction. 

fUse  50%  column  for  broken  stone  screened  to  uniform  size. 

jUse  45%  column  for  average  conditions  and  for  broken  stone  with  dust  screened  out. 

§Use  40%  column  for  gravel  or  mixed  stone  and  gravel. 


*Taken  by  permission  from  Taylor  &  Thompson's  "Concrete,  Plain  and  Reinforced,' 
copyright,  1905,  by  Frederick  W.  Taylor.    John  Wiley  &  Sons,  New  York,  publishers. 

18 


Per 


i 


"E  -*  O  rH         t-  rjl  T*        CJ  CO  t-        <N  OS 

^t>05oo      oqt-oo      t-oqoq      cqoq 


<N 

cqoq 
300         oo     o  do 


9*000     o  o  o 


iHrr  rHiH 


._ 

i 


portions  by  Volume 


3% 


Proportions  by  Pa 


^t>  os  oq     o^oq     oqooo)     oqo> 
s'ddd     odd     odd     do 


rHC4        OS  i-l  •*        rHOOO        <N  t> 

odd     odd     do 


•eON 


«Ot-O        Ofl  rH 

•*««     <NrH 

rHrHrH        rH  rH  t-*        r*  iH 


s'dd 
o 


o  oo 


rJtrHOO        Tj<O> 

WIOTH          10  TH 

s'ddd     odd     odd     do 


•IOTJ«O> 

300000 

-°  <N  (N  CN 


10  iH  •* 
|>IOCD 


N  rH  q      q  cq 

>r>rHrH        COrHlO        IO  t-*  O>        O>  N 
I        rHrH        rHrHrH        rHrHrH         rH  N 


ososos 


rHrn 


rHrHrH         rH  rH  rH        rH  rH  rH         rH  rH 


NOOCO        COW*       xJI"i«»0        100 


rHrHrH         r-T<N  CM        CN  <N  (N         COCO 


rH  rH  rH         rHrHrH        rHrHrH         rH  rH 


00«O 

C»T-J 

H  *     H          rH  i-J 


Ill 


Illll 

fc-l—  M-«0=* 


VOLUME  OF  PLASTIC  MORTAR  MADE  FROM  DIFFERENT  PROPORTIONS  OF  CEMENT 

AND  SAND* 
Quantities  of  Materials  per  Cubic  Yard 


Relative 
Proportions  by 
Volumef 

Volume  of  Compacted  Plastic 
Mortar 

Materials  for  1  cu.  yd.  Compacted 
Plastic   Mortar,  Based   on   Barrel 
of  3.8  Cubic  Feet 

Cement 

Sand 

From  1  cu.  ft.  Ce- 
ment, Based  on 
Portland  Cement 
Weighing  100 
Lbs.  per  cu.  ft. 

From  1  bbl., 
or  4  bags,  Ce- 
ment, Based  on 
Barrel  of  3.8  cu.  ft. 

Packed 
Cement 

Loose 
Sand 

1 
1 
1 

0 
1 
1H 

cu.  ft. 
0.86 
1.42 
1.78 

cu.  ft. 
3.2 
5.4 
6.7 

bbl. 
8.31 
5.01 
4.00 

cu.  yd, 

0.71 
0.84 

1 
1 
1 

2 

& 

2.14 
.     2.50 
2.86 

8.1 
9.5 
10.9 

3.32 
2.84 
2.48 

0.93 
1.00 
1.05 

Note. — Variations  in  the  fineness  of  the  sand  and  the  cement,  and  in  the  consistency  of  the  mortar  may  affect 
the  values  by  10%  in  either  direction. 
*See  reference,  footnote,  p.  18. 
fCement  as  packed  by  manufacturer,  sand  loose. 

RUBBLE  CONCRETE. 

Rubble  concrete  is  ordinary  concrete  in  which  are  imbedded  large  stones, 
usually  of  a  size  that  can  be  handled  by  one  or  two  men,  but  in  very  massive 
work  such  as  large  dams,  stones  of  even  greater  size  as  heavy  as  can  be  han- 
dled with  a  derrick  are  used.  Only  in  massive  structures  such  as  heavy  foun- 
dations, dams,  retaining  walls,  or  similar  works  is  this  form  of  construction 
possible  and  when  stones  are  imbedded  in  the  concrete  they  should  be  spaced 
at  least  3  inches  from  one  another  and  also  from  the  outer  surface.  About  20 
per  cent  of  the  total  volume  of  the  structure  may  be  replaced  by  "one-man" 
and  "two-men"  stones,  and  thus  a  considerable  saving  in  cost  is  effected  in 
large  structures. 

MIXING  CONCRETE. 

Mixing  may  be  done  either  by  hand  or  machine  and  the  method  to  be  em- 
ployed is  determined  principally  by  the  size  of  the  job.  If  a  small  amount  of 
concrete  is  to  be  made,  hand  mixing  is  the  more  economical,  while  for  large 
works  machine  mixers  are  better  and  generally  cheaper,  though  in  some  cases 
where  the  mixer  must  be  frequently  moved,  hand  mixing  may  prove  to  be  the 
cheaper.  A  better  and  more  uniform  concrete  can  be  made  with  a  good  ma- 


20 


chine  mixer  than  by  hand.  The  type  of  mixer  should  be  such  as  to  insure  a 
thorough  and  uniform  mixing  of  the  materials.  In  any  case  enough  water 
should  be  used  to  make  a  mushy  consistency  which  requires  very  little  tamp- 
ing to  bring  the  mortar  to  the  surface. 

HAND  MIXING. 

If  hand  mixing  is  employed  it  should  be  carefully  done  on  a  water-tight 
platform  and  should  be  subjected  to  thorough  supervision.  The  following  di- 
rections by  Taylor  and  Thompson  for  hand  mixing  will  be  found  useful  to 
those  who  are  inexperienced  in  this  class  of  work.* 


Turn 


FIG.  1.— POSITION  OF  MEN  AND  CONCRETE  ON  PLATFORM  WHILE  TURNING.* 

"Assume  a  gang  of  four  men  to  wheel  and  mix  the  concrete  with  two  other 
men  to  look  after  the  placing  and  ramming. 

"When  starting  a  batch,  two  mixers  shovel  or  wheel  sand  into  the  measur- 
ing box  or  barrel — which  should  have  no  bottom  or  top — level  it  and  lift  off 
the  measure,  leveling  the  sand  still  further  if  necessary.  They  then  empty 
the  cement  on  top  of  the  sand,  level  it  to  a  layer  of  even  thickness,  and  turn 
the  dry  sand  and  cement  with  shovels  three  times,  as  described  below,  after 
which  the  mixture  should  be  of  uniform  color. 

"While  these  two  men  are  mixing  sand  and  cement,  the  other  two  fill  the 
gravel  measure  about  half  full,  then  the  two  sand  men  take  hold  with  them, 
and  complete  filling  it.  The  gravel  measure  is  lifted,  the  gravel  hollowed  out 
slightly  in  the  center,  and  the  mixture  of  sand  and  cement  shoveled  on  top  in 
a  layer  of  nearly  even  thickness.f  A  definite  number  of  pails  are  filled  with 


*See  reference,  footnote,  page  18. 

t"Some  Engineers  prefer  to  spread  the  stone  on  top  of  the  sand  and  cement,  while 
others  prefer  to  mix  the  water  with  the  sand  and  cement  before  adding  them  to  the 
stone." 


21 


water,  and  poured  directly  on  the  top  of  these  layers,  greater  uniformity  being 
thus  attained  than  by  adding  the  water  directly  from  a  hose.  After  soaking 
in  slightly  the  mass  is  ready  for  turning. 

"The  method  illustrated  in  Fig.  i  of  turning  with  shovels  materials  which 
have  already  been  spread  in  layers  is  as  follows : 

"Two  men,  A  and  B,  with  square-pointed  shovels,  stand  facing  each  other 
at  one  end  of  the  pile  to  be  turned,  one  working  right-handed  and  the  other 
left-handed.  Each  man  pushes  his  shovel  along  the  platform  under  the  pile, 
lifts  the  shovelful,  turns  with  it,  and  then,  turning  the  shovel  completely  over, 
and  with  a  spreading  motion  drawing  the  shovel  toward  himself,  deposits  the 
material  about  2  feet  from  its  original  position.  Repetitions  of  this  operation 
will  form  a  flat  ridge  of  the  material,  on  a  line  with  the  pile  as  it  originally 
lay,  and  flat  enough  so  that  the  stones  will  not  roll.  As  soon  as,  but  not  be- 
fore, a  single  ridge  is  complete,  two  other  men,  C  and  D,  should  start  upon 
this  ridge,  turning  the  materials  for  the  second  time,  as  shown  in  the  illustra- 
tion, and  forming  as  before  a  flat  ridge  and  finally  a  level  pile  which  gradually 
replaces  the  last.  A  third  mixing  is  accomplished  in  a  similar  way. 

"Fig.  i  gives  the  position  of  the  piles  as  the  concrete  is  being  turned.  A 
portion  of  the  original  layers  is  shown  at  P,  the  ridge  formed  by  men  A  and 
B  shoveling  from  pile  P  is  shown  at  Q,  and  the  beginning  of  the  ridge  formed 
by  men  C  and  D  is  shown  at  RR.  The  third  turning  is  not  shown. 

"The  quantity  of  water  used  must  be  varied  according  to  the  moisture  in 
the  materials  and  the  consistency  required  in  the  concrete.  While  the  opin- 
ions of  engineers  regarding  the  proper  consistency  vary  widely,  it  is  advisable, 
the  authors  believe,  for  an  inexperienced  gang  to  use  an  excess  of  water.  The 
rule  may  be  made  in  hand  mixing  to  use  as  much  water  as  can  be  thoroughly 
incorporated  with  the  materials.  Concrete  thus  made  will  be  so  soft  or 
'mushy'  that  it  will  fall  off  the  shovel  unless  handled  quickly. 

"After  the  material  has  been  turned  twice,  as  described,  and  as  soon  as  the 
third  turning  has  been  commenced,  two  of  the  mixers  who  have  finished  turn- 
ing may  load  the  concrete  into  barrows  and  wheel  to  place.  They  should  fill 
their  own  barrows,  and  after  the  mass  has  been  completely  turned  for  the 
third  time  by  the  other  two  men  the  latter  should  start  filling  the  gravel 
measure  for  the  next  batch. 

"If  the  concrete  is  not  wheeled  over  50  feet,  four  experienced  men  ought 
to  mix  and  wheel  on  the  average  about  10%  batches  in  ten  hours.  This  figure 
is  based  on  proportions  1:2  %  '-5,  and  assumes  that  a  batch  consists  of  one 
barrel  (four  bags)  Portland  cement  with  9.5  cubic  feet  of  sand  and  19  cubic 
feet  of  gravel  or  stone. 

22 


"Assuming  that  1.29  barrels  of  cement  are  required  for  i  cubic  yard  of 
concrete,  one  barrel  of  cement — that  is,  one  batch — will  make  0.78  cubic  yard 
of  concrete;  hence  ioT/2  batches  mixed  and  wheeled  by  four  men  in  ten  hours 
are  equivalent  to  8%  cubic  yards  of  concrete.  This  is  for  the  very  simplest 
kind  of  concreting  and  makes  no  allowance  for  the  labor  of  supplying  ma- 
terials to  the  mixing  platform  or  for  building  forms." 

PLACING   CONCRETE. 

In  handling  and  placing  concrete,  the  materials  must  remain  perfectly  mixed, 
the  aggregate  must  not  separate  from  the  mortar  and  the  concrete  must  be 
rammed  or  agitated  so  as  to  thoroughly  fill  the  forms  and  surround  all  parts 
of  the  steel  reinforcement.  Care  must  be  taken  to  remove  all  sticks,  blocks, 
shavings,  or  similar  materials  from  the  forms  before  the  concrete  is  placed 
and  in  case  new  concrete  is  deposited  on  a  layer  that  has  already  set,  the  old 
surface  should  be  roughened,  cleaned,  and  drenched  with  water  before  the 
new  material  is  added.  In  reinforced  structures  the  metal  must  be  placed  in 
the  forms  and  wired  or  otherwise  held  rigidly  in  position  before  any  concrete 
is  laid.  It  is  now  generally  customary  to  use  wet  mixtures  and  the  concrete 
is  usually  carried  in  buckets  or  in  water-tight  wheelbarrows.  An  ordinary 
whelbarrow  load  of  concrete  is  about  1.9  cu.  ft.  If  wet  concrete  is  used  it 
can  be  dropped  vertically  into  place  or  run  through  an  inclined  water-tight 
chute.  Concrete  should  be  wet  frequently  for  a  few  days  after  it  is  laid. 


LAYING   CONCRETE   IN   WATER. 

Only  in  exceptional  cases  should  concrete  be  placed  in  water  and  even 
then  the  greatest  care  must  be  taken  to  prevent  the  cement  from  being  washed 
out.  Under  no  circumstances  should  it  be  thrown  or  placed  into  water  by 
shovels.  In  some  cases  of  small  construction,  the  concrete  may  be  deposited 
in  bags,  or  it  may  be  placed  in  pails  with  a  board  covering  the  top  of  the  pail 
and  lowered  carefully  into  the  water  to  the  bottom.  When  this  has  reached 
bottom,  turn  the  pail  upside  down  and  move  the  board  from  underneath  and 
carefully  raise  the  pail,  allowing  the  concrete  to  flow  out.  Great  care  must 
be  taken  not  to  disturb  the  water  in  which  the  concrete  is  being  placed  nor  to 
touch  the  concrete  before  it  has  set.  Under  no  circumstances  should  concrete 
be  placed  in  running  water.  In  large  work,  it  is  sometimes  placed  by  means 
of  a  tube  extending  into  the  water  with  the  lower  end  near  the  bottom.  By 
keeping  a  continuous  flow  of  concrete  passing  through  the  tube,  the  cement 
will  not  be  separated  from  the  aggregate. 

23 


LAYING  CONCRETE  IN  SEA  WATER. 

For  use  in  sea  water  concrete  must  be  proportioned  to  secure  maximum 
density  and  must  be  so  carefully  mixed  and  placed  as  to  secure  an  impervious 
mass.  Unless  proper  precautions  are  taken  in  choosing  the  materials,  mixing, 
and  in  depositing  the  concrete  there  is  danger  of  scaling  on  the  surface  of  the 
concrete  between  high  and  low  water  levels. 

The  remarks  just  made  concerning  the  use  of  concrete  in  sea  water  are 
equally  true  of  concrete  placed  in  alkaline  soils  where  the  mixture  must  be  of 
maximum  density  and  must  be  richer  than  where  used  in  ordinary  soils. 


EFFECT   OF   MANURE. 

Manure,  because  of  the  acid  in  its  composition,  is  injurious  to  green  con- 
crete, but  after  the  concrete  is  thoroughly  hardened  it  satisfactorily  resists 
such  action. 

FREEZING. 

Concrete  for  thin  walls  and  reinforced  concrete  structures  should  not  be 
laid  during  freezing  weather  unless  concrete  is  prevented  from  freezing  by 
warming  the  materials  before  mixing  and  by  covering  the  concrete  after  it  is 
placed  with  a  thick  covering  of  clean  straw,  sand,  or  other  suitable  material. 
Common  salt  is  quite  frequently  used  to  lower  the  freezing  point  of  the  water 
used  in  mixing  concrete.  A  well  known  rule  requires  i  per  cent  by  weight 
of  the  salt  to  the  weight  of  the  water  for  each  degree  Fahrenheit  below  freez- 
ing point  of  water. 

As  one  cannot  tell  in  advance  how  low  the  temperature  is  going  to  fall, 
an  arbitrary  amount  of  salt  must  be  used.  Some  engineers  specify  two  pounds 
of  salt  to  each  bag  of  cement,  and  in  case  this  is  not  sufficient,  three  pounds 
to  a  bag. 

Another  method  is  to  mix  warm  sand  and  stone  with  the  cement  and  water 
in  such  manner  as  will  bring  the  entire  mixture  up  to  about  75  degrees  Fahren- 
heit, protecting  in  the  early  stages  of  setting,  so  far  as  possible,  from  cold 
and  currents  of  air. 

Heavy  walls  and  foundations  where  the  appearance  of  the  faces  is  of  no 
importance  may  be  laid  in  freezing  weather. 

Concrete  sidewalks  must  not  be  laid  in  freezing  weather,  for  the  surface 
will  soon  scale. 

24 


FORMS. 

Forms  usually  are  of  wood,  though  in  some  cases  metal  is  used.  They 
must  be  strongly  built  so  as  to  prevent  displacement,  deflection,  or  leakage  of 
mortar  and  they  must  not  be  removed  until  the  concrete  has  set.  The  time 
required  for  setting  varies  with  the  condition  of  the  weather,  longer  time 
being  required  in  cold  or  wet  weather;  with  the  quality  of  the  cement;  and 
with  the  amount  of  water  used  in  mixing.  White  pine  is  the  best  lumber  for 
forms,  but  cheaper  kinds,  such  as  spruce,  fir,  Norway  pine  or  softer  kinds  of 
Southern  pine,  are  frequently  used,  and  green  lumber  is  on  the  whole  better 
than  dry.  To  secure  a  smooth  surface  on  the  finished  concrete,  lumber  planed 
on  one  side  must  be  used ;  likewise  where  the  forms  are  to  be  removed  within 
a  day  or  two,  planed  lumber  must  be  used,  for  then  the  concrete  will  not  stick 
to  the  planks  and  they  may  be  again  used  without  much  cleaning. 

Forms  usually  consist  of  boards  held  in  place  by  studs  braced  so  as  to 
remain  in  place.  For  the  boards  one  or  two-inch  planks  are  commonly  used 


FIG.  2.— FORMS  FOR  BEAM  BRIDGE 

and  quite  frequently  tongued  and  grooved  materials  are  necessary  for  tight 
construction.  The  studs  are  spaced  at  distances  apart  depending  upon  the 
consistency  of  the  concrete,  the  thickness  of  the  wall,  and  the  character  of 
finished  concrete  surface  desired.  Wet  concrete  in  large  masses  is  apt  to 
exert  considerable  pressure  against  the  forms  before  the  cement  sets,  but  with 
wet  concrete  less  ramming  is  necessary  than  with  dry  mixtures  and  therefore 
the  forms  are  less  likely  to  be  knocked  out  of  position.  With  wet  mixtures 
in  comparatively  thin  walls  two-inch  planking  should  be  supported  not  over 
5  feet  apart,  while  for  one-inch  boards  2  feet  is  about  the  right  spacing. 

Forms  are  greased  by  applying  to  them  a  coat  of  crude  oil  or  soft  soap, 
but  if  the  forms  are  not  to  be  removed  for  several  weeks  no  greasing  is  neces- 
sary, though  in  this  case  the  surfaces  of  the  forms  which  are  to  come  in  contact 
with  the  concrete  must  be  thoroughly  wet. 

25 


PAVEMENT  IN  CITY  OF  PANAMA. 


BRIDGE  NEAR  WASCO,  ILL. 
26 


CHAPTER  II. 

SIDEWALKS,  CURBS,  AND  GUTTERS. 

Concrete  is  in  universal  use  for  sidewalks,  curbs,  and  gutters,  and  the 
excellent  and  permanent  qualities  of  this  material  are  as  well  shown  in  these 
forms  as  in  any  other  type  of  construction  in  which  it  is  used.  Sidewalks 
should  be  smooth,  durable,  cheap  in  first  cost,  and  should  present  a  pleasing 
appearance.  With  proper  care  concrete  can  be  laid  to  satisfy  all  these  require- 
ments and  therefore  make  a  solid  durable  walk.  For  curbs  alone  or  for 
combined  curbs  and  gutters,  especially  for  the  streets  in  residential  districts, 
parks  or  similar  places  where  neatness  of  appearance  is  especially  desirable, 
concrete  is  being  used  in  many  localities  almost  exclusively.  In  this  chapter 
are  shown  methods  of  construction  which  are  standard  and  which  if  followed 
will  produce  good  results. 


FIG.  3— CROSS  SECTION  OF  SIDEWALK  AND  COMBINED  CURB  AND  GUTTER. 


DIMENSIONS  OF  WALKS,  CURBS,  AND  GUTTERS. 

A  first-class  walk  consists  of  a  foundation  of  cinders,  gravel,  or  broken 
stone  upon  which  is  laid  a  layer  of  concrete  called  the  base  and  an  upper  thin 
layer  of  mortar  called  the  wearing  surface.  Granolithic  is  a  common  name 
for  concrete  walks. 

Sidewalks  vary  in  width  according  to  conditions,  but  the  thickness  of  the 
concrete  is  nearly  uniform,  ranging  from  four  to  five  inches  total  thickness 
including  the  wearing  surface. 

In  Fig.  3  is  shown  the  section  of  a  sidewalk  separated  from  the  curb  by  a 
narrow  grass  plat  such  as  is  common  in  residential  streets.  The  thickness 
of  the  concrete  is  shown  as  5  inches,  but  4  inches  is  more  commonly  used, 
and  if  the  walk  is  provided  with  good  foundations  and  drainage  4  inches  is 
ample  in  most  places.  Where  the  total  thickness  of  the  concrete  is  4  inches 
the  base  should  be  3*4  or  3  inches  and  the  wearing  surface  */\  or  i  inch,  and 
for  a  5-inch  walk  the  base  should  be  4  inches  and  the  wearing  surface  i  inch. 

27 


The  slope  of  the  surface  from  the  lot  line  toward  the  curb  should  be  J4  or  H 
inch  per  foot.  For  parks  and  similar  locations  the  walk  is  usually  crowned 
toward  the  center. 

Curbs  are  made  from  6  to  8  inches  wide  on  top  and  are  generally  vertical 
on  the  side  next  to  the  walk  and  slightly  inclined  on  the  side  facing  the  gutter. 
The  total  depth  of  the  curb  should  be  from  12  to  14  inches,  and  if  the  street 
traffic  is  heavy  the  curb  should  set  upon  a  concrete  base  12  inches  wide  and  8 
inches  thick.  Where  the  curb  and  gutter  are  combined,  as  shown  in  Fig.  3, 
the  gutter  is  made  8  inches  thick  and  from  i^  to  3  feet  in  width.  In  the 
case  shown  the  curb  has  a  width  on  top  of  6  inches  and  tapers  down  to  6% 
inches  at  the  gutter.  Sometimes  both  the  inner  and  outer  surfaces  of  the 
gutter  are  made  vertical,  although  it  is  better  to  have  the  front  face  inclined. 
The  upper  outer  corner  of  the  curb  and  the  intersection  of  gutter  with  face  of 
curb  should  be  rounded  off  with  radii  of  about  i  inch. 

The  surface  of  the  gutter  should  conform  to  that  of  the  street  surface, 
though  in  some  cities,  as  for  instance  Salt  Lake  City,  the  upper  surface  of  the 
gutter  is  curved  in  such  a  manner  as  to  secure  greater  carrying  capacity,  the 
depth  of  the  gutter  being  10  inches,  whereas  it  would  be  only  8  inches  were 
the  curve  omitted  and  the  slope  of  the  street  continued  to  the  curb  line.  At 
street  corners  curbs  should  be  thicker  than  where  straight  so  as  to  better 
withstand  shocks  from  moving  vehicles.  Where  the  street  traffic  is  heavy,  the 
upper  outer  edge  of  the  curb  is  often  provided  with  a  special  steel  corner 
imbedded  in  the  concrete  as  it  is  laid. 

Fig.  4  illustrates  a  type  of  concrete  curb,  gutter,  and  cross  walk  construc- 
tion used  considerably  in  Chicago  on  streets  for  ordinary  traffic.  A  cross 
walk  is  provided  by  elevating  the  street  surface  near  the  curbs  as  shown. 


FOUNDATIONS   AND    DRAINAGE. 

A  good  foundation  properly  drained  is  absolutely  essential  for  successful 
sidewalk  construction,  and  is  best  made  by  excavating  the  soil  to  a  depth  of 
10  to  15  inches  below  the  level  of  the  finished  sidewalk  surface,  depending  on 
the  kind  of  soil  and  the  locality,  so  as  to  give  a  foundation  6  to  10  inches 
thick,  and  after  ramming  the  bottom  of  the  excavation  a  layer  of  coarse 
material  such  as  broken  stone,  cinders,  or  coarse  sand  is  placed  in  the 
excavation  and  thoroughly  rammed.  Drainage  and  ramming  are  of  the 
utmost  importance.  In  some  cities  no  foundation  is  required  in  soils  of 
clean  coarse  sand  which  is  porous  enough  to  afford  good  drainage,  while 
in  soils  which  retain  water  a  foundation  of  6  to  12  inches  is  specified. 
Fig.  3  shows  an  8-inch  foundation  of  cinders  under  the  walk  and  one  of  10 
inches  under  the  curb  and  gutter.  Broken  stone  or  gravel  should  be  screened 

28 


to  remove  all  fine  material  and  cinders  and  sand  should  be  wet  while  being 
rammed  into  place.  In  soils  like  clay  which  retain  water  the  foundation 
should  be  drained  by  running  occasional  drain  tiles  underneath  the  soil  from 
the  foundation  to  the  gutter,  or  other  suitable  outlet.  Instead  of  tile  drains 
small  ditches,  say  10  by  10  inches  in  cross  section,  filled  with  broken  stone 
may  be  used. 

PROPORTIONS  FOR  CONCRETE. 

Portland  cement  only  should  be  used. 

The  concrete  for  the  base  should  be  mixed  i  part  "ATLAS"  Portland 
Cement,  2^/2  parts  sand  or  fine  stone  which  will  pass  a  j4-inch  screen,  and  5 
parts  broken  stone  or  gravel  larger  than  J4  mch  size.  Where  the  quality  of 
the  sand  and  stone  require  it,  these  proportions  must  be  slightly  changed,  and 
if  the  sand  is  not  very  good  i  part  "ATLAS"  Portland  Cement,  2  parts  sand 
and  4  parts  stone  or  gravel  had  better  be  used. 

The  wearing  surface  should  be  mixed  i  part  "ATLAS"  Portland  Cement  to 
i  */2  parts  sand,  and  should  be  of  such  consistency  as  not  to  require  tamping, 
but  should  be  simply  floated  with  a  straight  edge.  The  sand  here  referred 
to  may  be  either  natural  bank  sand  or  crushed  stone  which  will  pass  a  ^4-inch 
screen  provided  it  is  from  a  hard  stone  which  has  but  little  dust. 

Another  excellent  plan  is  to  use  i  part  "ATLAS"  Portland  Cement  and  % 
part  sand  and  %  part  fine  crushed  stone. 

Although  i  part  cement  to  2  parts  fine  aggregate  is  quite  frequently  used 
for  the  wearing  surface  this  mixture  is  liable  to  make  a  surface  that  will  wear 
sandy. 

The  combined  curb  and  gutter  shown  in  Fig.  3  is  laid  on  a  cinder  founda- 
tion and  the  concrete  base  and  i-inch  finish  are  of  the  same  mixtures  as  speci- 
fied for  the  corresponding  parts  of  the  walk. 

FORMS. 

Forms  should  be  made  of  clean  lumber  not  less  than  2  inches  thick,  though 
i*/2  may  be  used  if  well  braced.  Fig.  5  shows  typical  form  construction  for 
walks  and  combined  curb  and  gutter.  The  walk  shown  is  5  inches  thick  and 
the  side  forms  are  2  by  6  inches,  although  2  by  5  inches  will  do  if  available. 
The  upper  edge  must  be  the  exact  level  of  the  finished  walk.  The  forms 
should  be  of  best  white  pine  planed  on  all  sides,  should  be  straight  and 
set  to  true  line  and  grade.  If  white  pine  is  too  expensive,  spruce,  fir,  or 
other  soft  woods  may  be  used.  The  wooden  pegs  should  be  spaced  from 
4  to  6  feet  apart  and  must  be  securely  driven  into  the  ground  so  that  the 
forms  will  not  move  while  concrete  is  being  deposited  against  them. 

30 


The  gutter  shown  as  5  inches  thick  in  the  drawing  is  suitable  for  streets 
with  light  traffic.  The  curb  is  6  inches  wide  and  1 1  inches  deep  with  both  faces 
vertical.  The  side  planks  are  held  in  place  by  the  wooden  pegs  and  the  front 
plank  for  the  curb  is  held  by  clamps  and  steel  dividing  plates,  the  latter  serv- 
ing as  spacers  as  well  as  dividing  plates  at  the  joints.  The  upper  corner  of 
the  curb  should  be  rounded  to  a  radius  of  i  inch  with  a  tool  and  the  lower 
corner  at  the  intersection  of  the  gutter  and  curb  should  be  similarly  arranged 
by  rounding  off  the  lower  inner  edge  of  the  front  plank  of  the  curb  form. 


pim^sML. 

j  j  Cf?ossS£cr/ow  or 


V 


FIG.  5.— FORMS  FOR  SIDEWALK  AND  COMBINED  CURB  AND  GUTTER 

PLACING   CONCRETE. 

After  having  placed  and  thoroughly  rammed  the  porous  foundation,  and 
having  carefully  set  the  forms  to  line,  as  described  above,  divide  the  surface 
into  blocks  by  cross  lines.  Mark  the  dividing  lines  between  the  blocks  on  the 
side  forms  by  notches  and  place  cross  strips  from  form  to  form  located  by 
these  notches.  The  blocks  should  be  nearly  square,  and  for  walks  4  inches  in 
thickness  should  not  be  over  6  feet  in  longest  dimension,  while  for  walks  5 
inches  in  thickness  8  feet  is  about  the  maximum  size.  By  laying  alternate 
blocks,  and  then  after  the  concrete  has  stiffened,  removing  the  cross  strips 
and  filling  in  the  blocks  between,  joints  are  made  so  that  if  the  walk  heaves 


FIG.  6.— CINDER  FOUNDATION  FOR  CONCRETE  SIDEWALK. 


FIG.  7.— PLACING  THE  CONCRETE  BASE. 
32 


slightly,  it  will  crack  in  the  joint  and  will  not  show,  provided  of  course  the 
wearing  surface  is  grooved  and  jointed  directly  above  the  joint  in  the  base. 

Mix  the  concrete  for  the  base  on  a  tight  platform  unless  the  street  pave- 
ment is  hard  and  impervious,  in  which  case  that  can  be  used  for  mixing. 
Make  the  consistency  rather  stiff,  but  wet  enough  so  that  the  concrete  will 
glisten  when  it  is  being  mixed,  and  although  holding  its  shape  in  a  pile,  can 
be  compacted  and  the  mortar  brought  to  the  surface  with  comparatively  light 
ramming.  See  that  the  surface  of  the  base  is  exactly  one  inch  below  the  upper 
level  of  the  forms,  so  that  the  wearing  surface  will  be  uniformly  one  inch 
thick.  To  accomplish  this,  make  a  straight-edge  of  %  inch  wood  notched  at 
each  end  to  fit  upon  the  forms. 

As  soon  as  a  few  blocks  of  the  base  have  been  laid,  and  before  the  concrete 
has  set,  mix  the  mortar  for  the  wearing  surface.  Make  this  one  part  "ATLAS" 
Portland  Cement  to  one  and  a  half  parts  sand  or  finely  crushed  stone  and  sand 
mixed.  This  mortar  may  be  mixed  in  a  mortar  box,  as  it  has  to  be  of  about 
the  consistency  of  mortar  for  laying  brick. 

To  secure  good  results  and  prevent  the  wearing  surface  from  eventually 
cracking  from  the  base,  it  is  absolutely  essential  that  the  mortar  be  spread 
before  the  concrete  base  has  begun  to  stiffen,  for  if  it  is  left  for  several  hours 
or  over  night  the  wearing  surface  is  almost  sure  to  peel  off  in  places. 

After  smoothing  the  wearing  surface  with  a  straight-edge,  float  it  roughly 
with  a  plasterer's  trowel,  and  after  a  few  hours,  when  the  mortar  has  begun  to 
stiffen,  float  it  with  a  wooden  float,  and  then  with  a  metal  float,  or,  as  it  is 
sometimes  called,  a  plasterer's  trowel.  Neat  cement  should  not  be  applied  to 
the  surface.  Just  as  the  final  floating  is  being  finished,  take  a  small  pointing 
trowel,  and  guided  by  the  notches  in  the  side  forms  and  by  a  straight-edge, 
placed  across  the  walk,  run  the  trowel  down  between  the  blocks  so  as  to  form 
a  joint  in  the  wearing  surface  directly  above  the  joint  in  the  base,  and  finish 
this  joint  with  a  groover,  so  as  to  give  it  rounded  edges.  The  side  edges  of 
the  walk  are  then  rounded  off  with  a  special  jointer,  and  the  surface  again 
finally  troweled. 

If  a  roughened  surface  is  desired,  a  dot  roller  or  a  grooved  roller  may  be 
used.  The  walk  should  be  protected  from  the  sun  for  at  least  four  days,  and 
wet  down  frequently. 

Curbs  and  gutters  should  be  laid  in  advance  of  the  walk  in  sections  5  or  6 
feet  in  length  and  a  joint  should  be  left  between  the  curb  and  the  walk.  The 
surface  of  the  gutter  and  the  top  and  front  surface  of  the  curb  should  be  made 
of  a  i -inch  layer  of  mortar  the  same  as  used  for  the  wearing  surface  of  the 
walk.  It  is  important  to  place  the  upper  part  of  the  curb  at  the  same  time 
with  the  lower,  for  the  perfect  union  of  the  two  parts  is  necessary  to  keep  the 
curb  in  position. 

33 


FIG.  8.— MIXING  MORTAR  FOR  WEARING  SURFACE. 


FIG.  9.— TROWELING  WEARING  SURFACE. 
34 


COLORING  MATTER. 

By  selecting  a  crushed  stone  of  the  proper  variety  a  permanent  color  can 
be  secured  for  the  surface  of  a  walk,  some  pink  granites  giving  especially 
pleasing  effects.  Artificial  coloring  matter  may  be  secured  by  the  addition 
of  lamp  black,  ochre,  iron  oxide,  and  other  materials  to  the  cement,  but  most 
of  these  colors  will  fade. 


MATERIALS  FOR  CONCRETE  SIDEWALKS,  FLOORS  AND  WALLS 


Bags  of  Cement  to  100  sq.  ft.  of  Surface 
area  of  Concrete  Base  or  of  Wall 

Bags  of  Cement  to  100  sq.  ft.  of  Mortar 
Surface 

Thick- 
ness, 
Inches 

Proportions 

Thickness, 
Inches 

Proportions 

1:1V2:3 

1:2:4 

1:3:6 

1:1 

iaw 

1:2 

3 
4 
5 
6 
8 
10 
12 

iff 

16  M 
22  M 
28  M 
34^ 

\^N^  \«  \N\N 
,H\  CON  i-i\  rHX,.^ 

CO  00  rH  CO  00  rH  CO 
rH  rH  rH  C4  CO 

I 

y2 
i  4 

!« 

5  2 
7 

10  4 

12 
14 

r 

1 

?| 

No.  of  sq.  ft.  of  Concrete  Laid  with 
4  Bags  (1  bbl.)  of  Cement 

No.  of  sq.  ft.  of  Mortar  Surface  Laid  with 
4  Bags  (1  bbl.)  of  Cement 

Thick- 
ness, 
Inches 

Proportions 

Thickness, 
Inches 

Proportions 

1:1^:3 

1:2:4 

1:3:6 

1:1 

i*M 

1:2 

3 

4 
5 
6 
8 
10 
12 

47 
36 
27 
24 
17 
14 
12 

60 
46 
36 
30 
22 
19 
15 

83 
66 
52 
41 
33 
26 
21 

M 

H 

1M  - 
1% 

1* 

114 
80 
57 
48 
40 
33 
29 

146 
100 
73 
60 
50 
43 
36 

178 
114 
89 
70 
59 
52 
44 

35 


QUANTITIES    OF   MATERIALS    FOR    SIDEWALKS. 

For  the  computation  of  the  quantities  of  cement,  sand,  and  stone  required 
to  construct  a  sidewalk  of  any  given  dimensions  the  accompanying  table  will 
be  found  useful  as  giving  the  quantities  required  to  lay  100  square  feet  of 
sidewalk.  The  values  given  are  based  on  a  barrel  of  3.8  cubic  feet  and  a 
coarse  aggregate  having  45  per  cent  voids  are  assumed.  In  the  table  allow- 
ances have  been  made  for  waste.  To  determine  the  total  volumes  required 
for  a  walk  of  given  proportions  and  dimensions  the  amounts  noted  for  the 
base  and  for  the  wearing  surface  should  be  added  together.  The  quantities 
required  will  of  course  vary  with  the  proportions  and  character  of  the  ma- 
terials. 


FIG.  10.— CONCRETE  SIDEWALK  IN  SOUTH  BETHLEHEM,  PA. 

COST. 

The  cost  of  sidewalks,  curbs  and  gutters  varies  with  the  locality,  size  of 
the  job,  and  with  the  character  of  the  soil  and  materials  used.  Work  finished 
recently  under  contract  for  Salt  Lake  City  shows  the  following  costs  to  the 
city.  These  figures  are  based  on  a  day's  work  of  eight  hours  and  laborers  at 
$2  per  day,  form  setters  $4  per  day.  Costs  given  below  are  per  linear  foot: 

Concrete  curb,  6  x  16  inches,  without  gutter $0.43 

Concrete  curb,  plain,  6  x  16  inches,  with  gutter  30  inches  wide 0.79 

Concrete  curb,  plain,  6  x  16  inches,  with  gutter  30  inches  wide  and  curved  to  special 

radius  0.85 

Concrete  curb,  6  x  16  inches,  reinforced,  without  gutter  and  curved  to  special 

radius  0.64 

Concrete  gutter,  30  inches  wide  along  curb 0.61 

36 


Mr.  George  W.  Tillson*  gives  the  cost  of  concrete  walks,  5  inches  thick 
and  laid  on  7  inches  of  cinders  in  Brooklyn,  N.  Y.,  as  16%  cents  per  sq.  ft. 

Fig.  10  shows  a  walk  built  of  "ATLAS"  Portland  Cement  in  South  Bethle- 
hem, Pa.,  where  the  current  price  for  walks  similar  to  that  shown  is  from  17  to 
20  cents  per  sq.  ft.  including  curb  and  gutter.  The  walk  is  4  feet  wide,  has  a 
3-inch  base  of  1 12 14  concrete  and  a  wearing  surface  of  i  :2  mortar,  and  is  laid 


_L  :^r_ 


FIG.  H.— CONCRETE  CROSS-WALK  OVER  GUTTER. 

on  an  1 8-inch  cinder  foundation.  The  front  face  of  the  curb  is  4  inches  high 
and  the  gutter  is  14  inches  wide  and  4  inches  thick.  Street  traffic  is  light  so 
that  heavy  curbs  and  gutters  are  not  required  at  this  location. 

Fig.  ii  and  Fig.  12  show  a  small  cross-walk  leading  from  a  front  walk  in  a 
yard  over  a  gutter  to  a  country  road.  The  walk  is  4  feet  in  width  and  the 
total  length  from  house  to  road  is  135/2  feet.  The  walk  in  the  yard  is  3  inches 


li 


i  • 


M 


FIG.  12.— CONCRETE  CROSS-WALK  OVER  GUTTER. 


*"Street  Pavements  and  Paving  Materials/'  p.  479. 

37 


thick,  and  on  each  side  of  the  circular  opening  is  12  inches  thick,  while  under 
the  opening  there  is  a  thickness  of  6  inches.  An  1 8-inch  cinder  foundation 
underlies  the  whole  work.  Two  cement  barrels  were  used  in  place  of  forms 
and  the  total  cost  of  the  walk  and  cross-walk  was  $13.20,  or  2454  cents  per 
sq.  ft. 

VAULT   LIGHT   CONSTRUCTION. 
In  Fig.  13  is  shown  a  design  for  vault  light  construction  supported  on 


FIG.  13.— TYPICAL  VAULT  LIGHT  CONSTRUCTION.* 


concrete  ribs  on  steel  I-beams.  The  sizes  of  the  concrete  ribs  and  the  steel  I- 
beams  depend  on  the  spans,  and  it  is  necessary  to  construct  the  concrete  ribs 
and  slab  at  one  time.  The  glass  discs  are  imbedded  in  the  concrete  and  admit 
light  to  the  area  below. 


*See  reference,  footnote,  page  18. 


CHAPTER  III. 

STREET   PAVEMENTS. 

The  ideal  street  pavement  is  durable,  noiseless,  cleanly,  easy  to  travel  on, 
low  in  first  cost,  and  built  of  such  material  that  the  maintenance  charges  are 
small.  Scarcely  any  material  has  been  found  which  entirely  satisfies  these 
requirements,  but  some  of  the  pavements  of  Portland  cement  concrete  which 
have  been  built  in  recent  years,  where  the  concrete  forms  not  only  the  founda- 


HASSAM  PAVEMENT,  PORTLAND,  OREGON. 

tion  but  also  the  wearing  surface,  are  giving  thorough  satisfaction  and  ap- 
proach closely  to  the  ideal  for  streets  where  the  traffic  is  not  so  excessive  as 
to  require  a  stone  block. 

For  pavement  foundations,  concrete  is  used  almost  universally  in  city 
streets  where  the  wearing  surface  is  asphalt,  brick,  wooden  blocks  or  stone 
blocks,  and  there  is  no  material  which  can  be  compared  with  it  for  this  pur- 
pose. Its  use  for  the  wearing  surface  is  comparatively  new,  but  it  is  proving 
its  usefulness  to  a  remarkable  degree. 

Concrete  sidewalks  made  of  a  concrete  base  with  a  granolithic  or  mortar 
wearing  surface  have  been  in  successful  use  ever  since  the  beginning  of  the 
Portland  cement  industry.  As  early  as  1894  alleys  were  paved  with  concrete 
in  Boston,  using  methods  similar  to  sidewalk  construction  except  slightly 

39 


thicker  layers  of  concrete  and  surface  divisions  into  small  blocks  instead  of 
large  ones,  so  as  to  give  better  footing  for  horses. 

Probably  the  first  street  pavement  of  concrete  was  built  in  Richmond, 
Ind.,  in  1903,  on  Sailor  Street,  and  in  1906,  when  it  was  necessary  to  cut  a 
trench  the  entire  length  of  this  pavement  for  telephone  conduits,  the  concrete 
was  found  so  hard  that  it  could  be  cut  only  with  great  difficulty.  On  the 
completion  of  the  conduit  the  pavement  was  repaired,  and  in  1908  it  seemed 
to  be  as  good  as  when  laid  in  1903. 

An  alley  pavement  in  Richmond  adjacent  to  the  Wescott  Hotel,  and  built 


BRIDGE    AT    HAWORTH,  N.  J. 

in  1896,  in  which  a  very  heavy  traffic  is  confined  to  a  small  space,  proved  so 
satisfactory  that  the  street  pavement  was  an  outgrowth  of  it.  An  examina- 
tion of  this  alley  in  1908  showed  the  surface  to  be  in  good  condition  with  very 
little  signs  of  wear. 

Concrete  street  pavements  contain  the  maximum  number  of  desirable 
qualities  as  compared  with  pavements  of  other  materials.  They  are  low  in 
first  cost,  since  the  materials  of  which  they  are  made  are  within  easy  reach 
of  all  localities  desiring  good  pavements.  Practically  no  section  of  the  coun- 
try is  without  stone  or  gravel  good  enough  for  the  main  body  of  the  pavement, 


40 


and  if  local  sand  is  too  poor  in  quality  and  freight  rates  prohibit  importing 
good  sand,  fine  crushed  stone  may  be  used  in  its  place.  "ATLAS"  Portland 
Cement  is  within  the  reach  of  every  section  of  the  country. 

The  quality  of  materials  and  workmanship  for  concrete  pavements  is  of 
greater  importance  than  in  almost  any  other  form  of  concrete  construction. 
The  aggregate  must  be  chosen  with  extreme  care,  the  cement  must  be  of  a 
first-class  standard  brand,  the  proportioning  of  the  materials  must  be  accurate, 
and  the  consistency  right.  Concrete  roadways  require  expert  workmanship 
but  no  more  so  than  the  laying  of  other  forms  of  pavement.  The  methods 
of  laying  and  the  materials  to  employ  are  best  understood  by  reference  to  the 
descriptions  given  in  the  pages  which  follow  of  pavements  which  have  proved 
successful.  Too  great  stress  cannot  be  laid  upon  the  matter  of  a  first-class 
aggregate  for  the  wearing  surface ;  if  this  cannot  be  obtained  concrete  street 
paving  should  not  be  attempted. 

The  maintenance  cost  of  concrete  pavements  is  very  low.  They  are  not 
injured  by  the  elements  or  by  materials  which  attack  some  forms  of  pave- 
ment. The  cost  of  maintenance  of  a  pavement  includes  the  cost  of  keeping  it 
clean  and  concrete  can  be  easily  cleaned  by  flushing  the  street  with  water, 
since  this  does  not  in  the  least  injure  the  quality  of  the  concrete  whereas  with 
some  other  pavements  constant  flushing  is  extremely  injurious. 

The  item  of  smoothness  is  to  a  large  degree  within  the  control  of  the 
builder  of  the  concrete  pavement;  for  the  surface  can  be  made  perfectly 
smooth  or  it  can  be  left  with  any  degree  of  roughness  by  grooving  the  surface 
or  otherwise.  Clearly,  on  a  steep  grade  the  pavement  should  be  left  so  that 
horses  can  get  a  foothold  and  on  curves  so  that  automobiles  will  not  slip. 
Both  of  these  conditions  can  be  met  by  grooving  or  roughening  the  wearing 
surface  of  the  concrete. 

A  wagon  running  over  a  concrete  pavement  makes  less  noise  than  running 
over  a  stone  block  or  other  similar  pavement  having  many  joints.  Another 
advantage  of  these  pavements  is  that  there  are  very  few  places  where  dust 
and  dirt  can  collect. 

Summing  up  then  the  advantages  of  concrete  pavements  it  is  seen  that 
they  offer  very  little  resistance  to  moving  vehicles,  afford  good  foothold  for 
horses  and  prevent  slipping  of  fast  moving  automobiles,  are  clean,  can  easily 
be  kept  free  from  dirt,  and  are  not  very  noisy.  A  pavement  combining  all 
these  desirable  qualities  is  certainly  one  that  should  commend  itself  to  those 
in  charge  of  construction  and  maintenance  of  our  city  streets. 

CONCRETE  STREET  PAVEMENT  FOUNDATIONS. 

Concrete  was  first  used  in  foundations  for  street  pavements  in  New  York 
City  in  1888.  At  the  present  time  nearly  all  cities  require  that  concrete  foun- 
dations shall  be  laid  under  all  classes  of  pavements.  It  is  well  understood 


that  the  success  of  any  pavement  depends  largely  upon  its  foundation.  To 
insure  a  good  foundation  the  subsoil  should  be  properly  shaped  and  graded 
and  then  thoroughly  rolled  with  a  steam  roller  weighing  not  less  than  10  tons. 
When  rolling  the  sub-grade  care  should  be  taken  to  remove  all  timbers  or 
other  matter  which  may  decay  and  leave  space  underneath  the  foundation. 
All  ditches  or  holes  must  be  filled  and  any  soft  material  removed  and  replaced 
by  good,  dry  gravel  or  similar  materials. 

PROPORTIONS  OF  CONCRETE  FOR  STREET  FOUNDATIONS. 

The  proportions  of  materials  for  concrete  to  be  used  in  foundations  for 
pavements  such  as  granite  blocks  or  asphalt  depend  upon  the  local  conditions. 
The  heavier  the  traffic  the  stronger  should  be  the  foundation.  The  propor- 
tions most  common  are  i  part  "ATLAS"  Portland  Cement,  3  parts  sand,  and 
from  5  to  7  parts  broken  stone  or  gravel.  In  most  cases  i  part  "ATLAS" 
Portland  Cement,  3  parts  sand,  and  6  parts  broken  stone  or  gravel  makes  a 
first-class  foundation.  The  thickness  of  foundations  of  Portland  cement  con- 
crete should  be  6  inches.  The  surface  of  the  concrete  should  be  kept  wet  for 
a  few  days. 

One  square  yard  of  concrete  foundation  6  inches  thick  will  require  1/6  of 
a  cubic  yard  of  concrete.  If  the  mixture  is  1 13  :6,  as  previously  specified,  the 
quantity  of  cement,  sand,  and  broken  stone  in  a  square  yard  of  foundation 
can  easily  be  determined  from  the  tables  of  quantities  in  Chapter  I,  page  19, 
by  dividing  the  quantities  given  by  6.  Thus,  for  i  square  yard  of  6-inch 
foundation  made  of  a  1:3:6  mixture  there  will  be  required  0.185  barrels  of 
cement,  0.078  cubic  yards  of  sand,  and  0.157  cubic  yards  of  stone.  These 
figures  are  based  on  average  conditions,  that  is,  45  per  cent  of  voids  in  the 
broken  stone.  Quantities  may  also  be  found  still  more  directly  from  table  in 
Chapter  II,  page  27. 

COST  OF  CONCRETE  FOUNDATIONS  IN  PLACE. 

The  cost  of  concrete  foundations  for  pavements  varies  greatly  with  the 
proportions  used  and  with  the  cost  of  the  materials  and  labor.  The  cost 
ranges  from  75  cents  to  $1.50  per  square  yard  for  the  usual  thickness  of  6 
inches.  The  following  is  an  estimate  for  the  cost  of  i  cubic  yard  of  i  :3 :6 
concrete  in  place  making  6  square  yards  of  finished  foundation.  For  other 
prices  of  materials  and  labor  the  items  may  be  varied  accordingly. 

Portland  Cement,  i.n  barrels,  $2.00 $2.22 

Sand,  0.47  cu.  yd.,  75  cents 0.35 

Broken  Stone,  0.94  cu.  yd.,  $1.75 1.65 

Labor  with  wages  at  20  cents  per  hour 1.15 

Cost  of  i  cubic  yard,  that  is,  6  square  yards  of  foundation  of  1:3:6  concrete 

in   place $5.37 

Cost  of  i  square  yard  of  6-inch  foundation 0.90 

42 


MIXING  OF   CONCRETE. 

Machine  mixing  gives  a  better  quality  of  concrete  than  hand  mixing,  but 
unless  a  large  area  is  to  be  concreted  and  the  machinery  is  very  carefully 
selected  and  arranged,  hand  mixing  is  apt  to  be  cheaper  and  is  therefore  more 
commonly  used.  For  hand  mixing  a  tight  matched  board  or  metal  platform 
should  be  used,  and  the  methods  should  conform  to  those  outlined  in  Chap- 
ter I.  The  consistency  of  the  concrete  may  be  somewhat  dryer  than  for  rein- 
forced concrete  work,  but  should  be  wet  enough  so  that  the  mortar  will  flush 
the  surface  with  a  very  little  ramming. 


FIG.  14.— CONCRETE  ROAD  AT  FLUSHING,  L.  I.,  N.  Y 

GANG  FOR  HAND  MIXED  CONCRETE. 

To  illustrate  the  arrangement  of  a  gang  in  street  pavement  foundation 
work,  the  following  example  is  taken  from  actual  practice:* 

Gang  for  a  6-inch  foundation  for  a  street  pavement,  where  the  sand  and  cement 
were  made  into  a  mortar  and  spread  on  to  the  stone,  and  where  two  mixing  platforms 
were  used,  one  on  each  side  of  the  street,  with  a  mortar  box  between  them. 
"One  foreman. 

"Two  men  mixing  mortar  in  one  mortar  box. 
"Four  men  shoveling  stone  alternately  into  two  measuring  boxes. 
"Four  men  working  alternately  on  the  two  mixing  platforms,  spreading  mortar 
on  stone,  mixing  concrete,  and  shoveling  to  place. 

"Three  men  leveling  and  ramming  concrete,  and  also  assisting  to  shovel  to  place. 
"One  man  carrying  water  and  doing  other  odd  work. 

"The  total  quantity  of  concrete  in  proportions  1:2:5  laid  per  day  of  ten  hours  aver- 
aged from  40  to  46  batches  or  29  to  33  cubic  yards  per  day  for  the  gang.  The  gang 
was  not  quite  up  to  the  average,  for  under  given  conditions  they  ought  to  have  turned 
out  regularly  34  cubic  yards  per  day  of  ten  hours." 


*See  reference,  footnote,  page  18. 


43 


CONSTRUCTION  OF  FOUNDATIONS. 

The  whole  operation  of  mixing  and  depositing  concrete  in  pavement  foun- 
dations should  be  carried  on  as  quickly  as  is  possible  with  thoroughness. 
Concrete  which  has  been  mixed  and  has  set  or  hardened  to  any  extent  should 
not  be  allowed  to  be  used  in  the  foundation.  Wherever  possible  the  concrete 
should  be  laid  entirely  across  the  street  without  longitudinal  joints.  Boards 
set  to  proper  elevation  and  curved  on  the  upper  edge  to  conform  to  the  cross 
section  of  the  foundation  are  set  across  the  street  and  between  these  forms 
the  concrete  is  laid. 

When  connection  is  to  be  made  with  any  section  which  has  been  previously 
laid  and  which  is  partially  or  wholly  set  the  edge  of  such  section  must  be 
broken  off  so  as  to  be  vertical,  and  must  be  freed  from  dirt  and  properly  wet 
before  fresh  concrete  is  laid  against  it.  No  carting,  wheeling,  walking  or 
bicycle  riding  should  be  allowed  on  the  concrete  until  it  has  hardened. 

The  top  surface  of  all  concrete  foundations  should  be  left  rough  so  as  to 
better  hold  the  wearing  surface  which  is  placed  upon  it.  Expansion  joints 
may  be  left  at  intervals  not  over  100  feet  lengthwise  of  the  street.  They  can 
be  made  best  by  setting  in  the  concrete  a  i-inch  board  upright  on  its  edge 
across  the  street  from  the  curb  to  curb  and  after  the  concrete  is  sufficiently 
hardened  the  board  is  removed  and  the  space  filled  with  coarse  or  fine  gravel. 
Expansion  joints  are  especially  necessary  near  a  change  in  grade  of  the  street 
where  expansion  from  heat  may  cause  the  pavement  to  buckle  upward. 

CROWNING  OF  ROADWAYS. 

The  finished  surface  of  all  roadways  should  be  higher  at  the  center  than 
at  the  gutters  to  afford  good  drainage.  Although  engineers  do  not  entirely 
agree  as  to  the  proper  amount  of  this  crowning,  practically  all  agree  that  the 
upper  surface  of  the  sub-grade  and  of  the  foundation  should  be  crowned  to 
conform  to  the  upper  finished  surface  of  the  street  pavement.  Crowning  is 
necessary  on  all  streets  and  for  all  materials  and  the  smallest  crown  which 
will  properly  drain  the  street  surface  is  best. 

The  top  of  the  sub-grade  is  always  below  the  surface  of  the  finished  pave- 
ment by  an  amount  equal  to  the  thickness  of  the  pavement  and  its  cushion, 
if  any,  plus  the  thickness  of  the  concrete  foundation. 

In  addition  to  crowning  of  the  surface  the  street  should  have  a  longitudinal 
grade  so  that  water  can  be  carried  off.  This  grade  should  not  be  less  than 
0.3  feet  or  4  inches  in  100  feet  for  hard  materials  such  as  pavements  of  concrete 
or  good  macadam.  Where  the  street  is  level  the  longitudinal  drainage  must 
be  secured  by  giving  a  grade  to  the  gutters  between  catchbasins.  This  neces- 
sitates varying  the  crown  along  the  street. 

44 


For  widths  of  roadways  between  curbs  of  24,  30,  36,  48,  and  60  feet  the 
crown  should  be  3,  4,  5,  6,  and  8  inches  respectively;  the  inches  given  being 
the  difference  in  elevation  of  the  finished  wearing  surface  at  the  center  of  the 
street  and  at  each  curb. 

The  cross  section  of  the  street  surface  is  curved  and  points  on  this  curve 
can  most  easily  be  located  by  driving  stakes  at  the  center  of  the  street,  at 
each  curb  and  at  points  1/3  and  2/3  distant  from  the  center  to  the  curb  on 
either  side.  The  tops  of  these  stakes  can  be  located  in  the  following  manner : 
Stretch  a  string  across  the  street  so  that  it  will  be  level  at  the  proper  eleva- 
tion of  the  upper  finished  surface  of  concrete  foundation  at  the  center  of  the 
roadway.  Compute  the  ordinates  from  the  string  to  the  elevation  of  the 
finished  surface  of  foundation  at  points  1/3  and  2/3  of  the  distance  from  the 
center  toward  each  curb.  The  ordinate  to  be  measured  down  at  the  1-3  point 
nearest  the  center  is  equal  to  1/9  of  the  amount  of  crown  determined  upon 
and  the  ordinate  to  be  measured  down  at  the  2/3  point  from  the  center  is  4/9 
of  the  total  crown.  This  is  illustrated  in  the  accompanying  table.  Thus, 

TABLE  OF  OFFSETS  FOR  CROWNING  STREETS  OF  VARIOUS  WIDTHS, 


Width  of 

Distance  From 

Distance  From 

Roadway  Be- 

Crown 

Center  of 

Vertical  Offset 

Center  of 

Vertical  Offset 

tween  Curbs 

Roadway 

Roadway 

Feet 

Inches 

Feet 

Inches 

Feet 

Inches 

24 

3 

4 

% 

8 

1% 

30 

4 

5 

% 

10 

1% 

36 

5 

6 

% 

12 

2% 

48 

6 

8 

% 

16 

2% 

60 

8 

10 

% 

20 

3% 

for  a  roadway  24  feet  wide  having  a  crown  of  3  inches  the  elevation 
of  the  finished  surface  of  foundation  at  points  4  feet  on  either  side  of 
the  center  should  be  1/9  of  3  inches,  that  is,  1/3  inch  below  the  level 
string,  which  corresponds  with  the  elevation  of  the  upper  surface  of 
concrete  foundation  at  the  center.  At  points  8  feet  out  on  either  side  of  the 
center  of  the  roadway  the  elevations  of  the  finished  surface  of  foundation 
should  be  4/9  of  3  inches,  or  i  1/3  inches,  below  the  string.  The  gutter  of 
course  would  be  3  inches  below  the  surface  at  the  center  where  the  crown  is 
3  inches  as  here  assumed.  The  grade  of  the  sidewalk  next  to  the  property 
line  is  frequently  made  the  same  as  the  center  of  the  street. 

Transverse  rows  of  stakes  similar  to  those  just  described  are  placed  every 
10  to  25  feet  apart  lengthwise  of  the  street.  Of  course,  these  stakes  should  be 
driven  in  after  the  sub-grade  is  thoroughly  rolled  and  shaped  so  that  they 
will  be  parallel  to  the  finished  surface  of  street. 


45 


The  curbs  should  always  be  set  to  line  and  grade  before  the  foundation 
for  the  pavement  is  laid. 

FOUNDATIONS  UNDER  STREET  RAILWAY  TRACKS. 

When  a  street  or  a  portion  of  a  street  under  improvement  is  occupied  by 
street  railway  tracks  and  the  tracks  are  removed  during  construction  work, 
the  excavation  of  that  portion  of  the  street  occupied  by  the  tracks  should  be 
made  to  a  depth  of  6  inches  below  the  bottom  and  6  inches  beyond  the  ends 
of  the  ties.  The  remainder  of  the  excavation  must  correspond  in  depth  to 
that  required  for  the  ordinary  pavement.  The  concrete  along  the  track  is 
then  laid  to  a  thickness  of  6  inches  below  the  bottom  of  the  ties.  The  ties 
and  rails  are  set  in  place  upon  this  layer  and  brought  to  true  line  and  grade. 
Additional  concrete  should  be  tamped  under  and  around  the  rails  and  thor- 
oughly grouted  with  a  grout  made  of  i  part  "ATLAS"  Portland  Cement  to 
2  parts  clean,  sharp  sand.  In  case  concrete  beam  construction  is  used,  that  is, 
where  a  rectangular  beam  of  concrete  is  laid  longitudinally  under  each  rail, 
the  excavation  must  conform  to  special  plans  for  the  track  construction. 

For  sheet  asphalt  pavements  the  top  of  the  concrete  foundation  should  be 
parallel  with  and  3  inches  below  the  finished  surface  grade.  For  stone  block 
pavements  to  allow  for  6-inch  block  and  2-inch  sand  cushion  the  top  of  the 
concrete  is  8  inches  below  the  finished  surface  of  the  pavement.  Brick  pave- 
ments are  usually  4  inches  thick  and  are  laid  with  a  2-inch  sand  cushion 
between  the  bottom  of  bricks  and  top  of  concrete  foundation  so  that  the  con- 
crete is  6  inches  below  the  finished  grade. 


CONCRETE   PAVEMENTS. 

The  use  of  concrete  for  the  wearing  surface  of  a  pavement  as  well  as  for 
the  foundation  is  comparatively  recent.  The  examples  of  these  pavements 
already  built  have  proved  so  successful  that  the  increase  in  this  class  of  con- 
struction will  undoubtedly  be  very  rapid.  If,  as  has  been  indicated,  proper 
care  is  used  in  the  selection  of  the  materials  and  in  the  workmanship,  such 
pavements  will  prove  satisfactory  and  durable. 

Concrete  pavements  have  been  successfully  built  by  several  cities  as  de- 
scribed in  the  pages  which  follow,  and  patented  types  of  pavement,  the  Blome 
and  the  Hassam,  have  also  been  laid  in  various  places.  Pavements  built  in 
Richmond,  Ind.,  and  other  cities,  have  been  made  by  similar  methods  to  those 
employed  for  first-class  sidewalk  construction,  using  a  compacted  and  well 
drained  foundation  of  concrete  and  a  mortar  wearing  surface.  The  Blome 
pavement  is  similarly  made  with  a  concrete  foundation  and  a  concrete  wearing 

46 


surface,  using  specially  selected  materials  and  having  the  surface  divided  into 
blocks.  The  Hassam  pavement  usually  consists  of  well  compacted  layers  of 
broken  stone  with  the  voids  filled  with  Portland  cement  grout  and  thoroughly 
rolled. 


FIG.  15.— BLOME  GRANITOID  PAVEMENT,  OHIO  STREET,  CHICAGO. 


ESSENTIALS   OF  A   CONCRETE   PAVEMENT. 

In  order  that  a  concrete  pavement  shall  prove  satisfactory  tne  following 
essentials  must  be  adhered  to : 


(1)  Thoroughly  compacted  sub-foundation. 

(2)  Foundation  (unless  the  soil  is  very  porous)   of  porous  materials  rolled  or 

otherwise  compacted. 

(3)  A  base  of  first-class  Portland  cement  concrete. 

(4)  A  wearing  surface  composed  of  a  standard  Portland  cement  and  a  carefully 

selected  aggregate. 

(5)  Expert  and  very  careful  workmanship. 

The  fine  aggregate  for  the  surface  layer  is  of  the  utmost  importance.  Per- 
haps the  best  material  is  crushed  granite  or  crushed  trap  whose  particles  pass 
a  ^4-inch  sieve  and  which  contains  scarcely  any  dust.  Sand  may  be  used  pro- 

47 


vided  it  is  of  exceptionally  good  quality,  coarse,  clean,  free  from  clay  or  other 
fine  matter,  and  absolutely  free  from  vegetable  loam.  In  natural  sand  the 
percentage  of  dust  passing  a  sieve  having  100  meshes  per  linear  inch  might 
well  be  limited  to  3  per  cent. 

BLOME  CO.  GRANITOID  CONCRETE  PAVEMENT. 

Pavements  made  entirely  of  concrete  are  coming  more  and  more  into  gen- 
eral use  as  the  true  strength  and  worth  of  concrete  is  becoming  better  known 
and  understood.  One  of  the  all-concrete  pavements  is  known  as  the  Blome  Co. 
Patented  Granitoid  Pavement  and  is  laid  under  patents  owned  by  the  Rudolph 
S.  Blome  Company  of  Chicago.  As  previously  stated  the  Blome  Co.  Granitoid 
pavement  consists  of  a  lower  layer  of  concrete  serving  as  a  base  and  an  upper 
thinner  layer  of  richer  concrete  forming  a  wearing  surface ;  the  two  layers  be- 
ing laid  so  as  to  secure  a  perfect  union,  thus  forming  a  monolith.  The  upper 
surface  is  grooved  to  give  a  good  foothold  for  horses. 


W/dfh  of  ^/reef 


'••"'  foc/ndor/bn  //?  ca^e  of  c/ay 
Aeaisy 


FIG.  IS.— STANDARD  SECTION  BLOME  CO.  PATENTED  GRANITOID  PAVEMENT. 


Fig.  1 6  shows  a  standard  section  of  the  Blome  Co.  Granitoid  Pavement.  It 
consists  of  a  sJ^-inch  thickness  of  concrete  with  a  i^-inch  surface  of  a  richer 
concrete,  the  two  layers  being  laid  so  as  to  give  it  thorough  union.  The 
drawing  shows  a  foundation  of  sand,  gravel,  broken  stone  or  cinders  which 
is  necessary  where  the  soil  is  clay  or  hard  pan  or  in  fact  in  any  soil  except  a 
porous  sand  or  gravel.  Expansion  joints,  %  inch  wide,  are  left  along  the 
gutters  or  curbs. 

The  granitoid  pavement  has  been  laid  in  many  places  and  has  given  very 
good  satisfaction.  It  presents  a  gritty  surface  and  affords  an  excellent  foot- 
hold for  horses.  On  wet  slippery  streets  horses  travel  more  freely  and  easily 
on  the  granitoid  pavement  than  on  other  more  smooth  and  equally  hard  pave- 
ments. Granitoid  has  been  used  successfully  on  8  per  cent  grades  at  Knox- 
ville,  Tennessee;  on  streets  in  Michigan  where  the  temperature  falls  at  times 

48 


to  40  degrees  below  zero ;  and  on  streets  in  the  South  where  the  pavement  is 
subjected  to  intense  heat.  Granitoid  pavements  have  demonstrated  that  when 
properly  laid  concrete  is  not  seriously  affected  by  temperature. 

GENERAL  SPECIFICATIONS  FOR  THE  BLOME  COMPANY 
GRANITOID  CONCRETE  BLOCKED  PAVEMENT. 

The  following  general  specifications  have  been  furnished  through  courtesy 
of  the  Rudolph  S.  Blome  Company  of  Chicago. 

PREPARATION  OF  SUB-GRADE.— The  street  shall  be  graded  (excav- 
ated or  filled  as  the  case  may  be)  to  sub-grade,  including  compacting  and 
rolling  by  means  of  a  heavy  steam  roller,  and  all  slopes,  contours  and  other 
shaping  required  in  the  finished  pavement  shall  be  formed  and  provided  for 
in  said  sub-grade,  so  that  the  foundation  and  pavement  hereinafter  specified 
will  be  uniformly  of  the  same  thickness  throughout.  The  contractor  to  use 
extreme  care  to  remove  all  spongy  material  or  other  unsuitable  or  vegetable 
matter  that  may  be  in  the  way  of  making  this  improvement  a  permanent  one. 

The  contractor  will  bid  with  the  strict  understanding  that  he  or  they  must 
use  all  necessary  precautions  in  preparing  the  sub-grade,  so  as  to  support 
the  pavement  permanently,  and  so  that  the  pavement  shall  remain  at  the 
original  grade  for  a  period  of  five  years.  This  clause  shall  not  be  waived  on 
account  of  any  trenches  or  holes  dug  in  the  street  by  any  corporation  or 
private  party,  prior  to  the  laying  of  the  pavement. 

FOUNDATION.— Where  the  natural  soil  is  of  sandy  or  gravelly  nature,  no 
other  foundation  will  be  required,  but  where  the  natural  soil  is  clay,  the  con- 
tractor shall  grade  for  and  provide  a  foundation  of  sand,  gravel,  crushed  stone 
or  other  suitable  material,  and  which  foundation  after  having  been  flooded 
and  compacted,  satisfactory  to  the  engineer,  shall  be  not  less  than  3  inches 
thick. 

MATERIALS. — Samples  of  the  cement  which  is  proposed  to  be  used  in 
the  work  shall  be  submitted  to  the  engineer  in  such  quantities  and  at  such 
time  and  place  as  will  enable  him  to  make  all  required  tests.*  The  engineer 
reserves  the  right  to  reject  without  recourse  any  cement  which  is  not  satis- 
factory, whether  for  reasons  mentioned  in  these  specifications  or  for  any  good 
and  sufficient  cause. 

All  the  cement  to  be  used  must  be  delivered  on  the  work  in  approved 
packages,  bearing  the  name,  brand  or  stamp  of  the  manufacturer.  It  shall  be 
thoroughly  protected  from  the  weather  until  used  in  such  manner  as  may  be 
directed. 

SAND. — All  sand  shall  be  clean,  dry,  free  from  dust,  loam  and  dirt,  of 
sizes  ranging  from  %  inch  down  to  the  finest,  and  in  such  proportions  that 

^Specifications  for  the  cement  are  also  included. 

49 


the  voids,  as  determined  by  saturation,  shall  not  exceed  33  per  cent  of  the 
entire  volume,  and  it  shall  weigh  not  less  than  95  pounds  per  cubic  foot.  No 
wind  drifted  sand  shall  be  used. 

CRUSHED  STONE.— All  crushed  stone  used  in  making  the  concrete  shall 
be  of  the  best  quality  of  limestone,  trap  rock  or  granite,  clean,  free  from  dirt, 
broken  so  as  to  measure  not  more  than  1^2  inches  and  not  less  than  %  incn  m 
any  dimension.  The  stone  when  delivered  on  the  street  shall  be  deposited 
on  flooring  and  kept  clean  until  used. 

GRAVEL. — If  gravel  is  used,  same  to  be  perfectly  clean  gravel,  free  from 
all  loam  and  foreign  substances,  and  the  same  size  as  that  specified  herein  for 
crushed  stone. 

MIXING  AND  LAYING  OF  CONCRETE  AND  FORMATION  OF  THE 
BLOME  COMPANY  GRANITOID   BLOCKING. 

The  concrete  and  blocking  hereinafter  specified  shall  be  constructed  and 
manipulated  according  to  the  Blome  Company  patents  and  processes,  using 
materials  mixed  in  the  proportions  and  laid  as  hereinafter  specified. 

The  pavement  shall  consist  of  5*4  inches  of  concrete,  and  surface  blocking 
1 54  inches,  making  a  total  of  7  inches,  exclusive  of  foundation. 

After  the  sub-grade  and  foundation  have  been  prepared  as  hereinbefore 
specified,  there  shall  be  deposited  concrete  composed  of  i  part  of  Portland 
cement,  3  parts  sand,  and  4  parts  of  crushed  limestone,  trap  rock,  or  clean 
gravel.  These  materials  to  comply  with  the  requirements  hereinbefore  set 
forth  and  shall  be  mixed  by  special  mixing  machine  suitable  for  the  purpose 
to  be  approved  by  the  engineer  and  shall  be  mixed  at  least  five  times  before 
being  removed  from  the  mixer.  The  concrete  shall  be  thoroughly  tamped  in 
place,  and  shall  be  5%  inches  thick,  uniformly  at  all  points,  after  having  been 
compacted,  shall  be  laid  in  sections  with  expansion  joints,  all  as  per  the  Blome 
Company  patents  and  shall  follow  the  slopes  of  the  finished  pavement  so  that 
the  surface  blocking  is  and  shall  be  uniformly  of  the  same  thickness  at  all 
points. 

SURFACING  MATERIAL.— After  the  concrete  has  been  placed  and 
before  it  has  begun  to  set,  there  shall  be  immediately  deposited  thereon  the 
Granitoid  Blocking  which  shall  be  i^4  inches  in  thickness  to  be  composed  of 
two  parts  of  the  hereinbefore  specified  Portland  cement  and  three  parts  of 
clean,  crushed  granite,  trap  rock,  hard  stone,  crushed  gravel,  crushed  boulders, 
or  other  similarly  hard  materials  shall  be  screened  with  all  the  dust  removed 
therefrom  utilizing  the  following  composition  of  this  material. 

Fifty  per  cent  of  the  granite,-  trap  rock,  hard  stone,  crushed  gravel,  crushed 
boulders  or  other  similarly  hard  materials  to  be  what  is  known  as  j4-inch  size, 

50 


30  per  cent  of  the  */s-inch  size,  and  20  per  cent  of  the  i-i6-inch  size  with  all 
finer  particles  removed.  These  proportions  of  sizes  are  extremely  essential 
and  must  be  kept  absolutely  accurate  as  in  this  lies  one  of  the  essential  re- 
quirements to  produce  proper  results.  This  material  to  be  mixed  with  cement 
thoroughly  and  after  being  wetted  to  a  proper  consistency  and  deposited  on 
the  concrete  shall  be  worked  into  brick  shapes  of  approximately  4^4  inches  by 
9  inches  with  rectangular  surface  similar  to  paving  blocks,  all  as  per  special 
method  and  utilizing  grooving  apparatus  as  employed  under  the  Blome  Com- 
pany patents.  The  pavement  shall  be  sloped  in  a  manner  as  required  by  the 
City  Engineer. 

Should  there  be  any  part  or  parts  of  this  pavement  when  completed  where 
the  slopes,  contours,  etc.,  have  not  been  carried  out  in  true  manner  then  under 
this  specification  the  contractor  will  be  required  to  take  up  such  part  or  parts 
down  to  the  foundation  and  replace  same  to  the  proper  level  without  expense 
of  any  kind  to  the  city. 

EXPANSION  JOINTS.— The  contractor  for  the  work  above  specified 
shall  also  be  required  to  provide  for  expansion  joints  across  the  pavement  at 
such  locations  as  may  be  necessary,  which  expansion  joints  shall  extend 
through  the  blocking  and  concrete  and  shall  be  filled  with  a  composition 
especially  prepared  for  the  purpose  according  to  the  Blome  Company  patents. 
These  expansion  joints  shall  be  constructed  in  an  extremely  careful  manner 
under  specific  direction  of  the  City  Engineer. 

PATENTS. — All  fees  for  any  patent  invention,  article  or  arrangement  or 
other  apparatus  that  may  be  used  upon  or  in  any  way  connected  with  the  con- 
struction, erection,  or  maintenance  of  the  work  or  any  part  thereof,  embraced 
in  the  contract  on  these  specifications  shall  be  included  in  the  price  stipulated 
in  the  contract  for  said  work,  and  the  contractor  or  contractors  must  protect 
and  hold  harmless  the  city  against  any  and  all  demands  for  such  fees  or  claims. 

GUARANTY. — Upon  the  completion  of  the  contract,  the  contractor  shall 
furnish  a  satisfactory  surety  company  bond  executed  by  one  of  the  Surety 

Companies  in  good  standing  in  the  State  of ,  guaranteeing  the 

pavement  mentioned  against  settlements,  upheavals,  disintegration  and  the 
results  of  faulty  workmanship,  and  the  use  of  materials  of  improper  quality 
for  and  during  the  period  of  five  years  from  and  after  the  date  of  completion 
of  the  pavement. 

It  is  to  be  expressly  understood  that  the  above-mentioned  pavement  shall 
satisfactorily  withstand  all  severe  usage  to  which  same  will  be  subjected  dur- 
ing and  for  the  period  named  above. 

BIDDERS'  ATTENTION.— The  attention  of  the  bidders  is  called  to  the 
following  copy*  of  agreement  in  the  offices  of  the  City  Clerk  for  furnishing 

*Not  here  given. 

51 


necessary  materials  and  mixtures  for  laying  the  surfacing  material  of  the  con- 
templated pavements  and  for  the  allowance  of  the  uses  of  certain  patented 
processes  owned  and  controlled  by  the  Blome  Company  and  for  the  expert 
advice  which  will  be  furnished,  which  agreement  forms  a  part  of  these  speci- 
fications and  which  must  be  considered  as  a  requirement  by  prospective  bid- 
ders in  the  making  up  of  their  proposals  on  the  contemplated  work. 


FIG.  17.— BLOME  CO.  GRANITOID  PAVEMENT,  KNOXVILLE,  TENN. 

COST  OF  BLOME  CO.  GRANITOID  PAVEMENT. 

The  cost  of  this  pavement  varies  greatly,  depending  upon  location,  quan- 
tity of  work,  costs  of  the  various  materials  and  labor.  The  price  ranges  from 
$1.50  to  $3  per  square  yard,  not  including  excavation  or  grading.  Its  use 
compares  favorably  in  cost  with  brick,  asphalt,  or  creosote  or  wooden  blocks 
on  concrete  foundations. 

In  Knoxville,  Tenn.,  the  same  granitoid  laid  in  accordance  with  methods 
previously  described  cost  $1.88  per  square  yard  in  place,  exclusive  of  the  grad- 
ing, which  varied  from  15  to  20  cents  per  square  yard  of  pavement,  making 
the  total  cost  of  finished  pavement  from  $2.03  to  $2.08  per  square  yard. 

In  New  Haven,  Conn.,  the  Blome  pavement  has  been  laid  at  $2.25  per 
square  yard. 

52 


A  piece  of  granitoid  block  laid  on  48th  Avenue,  Hawthorne,  111.,  in  the 
fall  of  1904,  was  in  very  good  condition  when  examined  in  January,  1909. 
This  pavement  is  7  inches  thick  and  cost  $3  per  square  yard  exclusive  of 
excavation  or  grading. 

HASSAM  PAVEMENT. 

Hassam  pavements  are  laid  in  the  form  of  a  grouted  macadam  street  or  as 
a  granite  block  pavement  on  a  grouted  macadam  foundation.  In  each  case 
the  work  is  done  in  a  manner  peculiar  to  this  type  of  pavement. 


FIG.  18.— HASSAM  PAVEMENT,  BIDDEFORD,  MAINE. 

HASSAM   GROUTED   CONCRETE  PAVEMENT. 

The  Hassam  pavement  as  usually  laid  consists  of  a  properly  compacted 
sub-grade  upon  which  is  placed  a  layer  of  broken  stone  thoroughly  rolled  to 
a  thickness  of  six  inches  and  made  to  conform  to  the  grades  and  cont9ur  of 
the  street.  After  this  stone  has  been  firmly  compacted  by  rolling  and  the 
voids  reduced  to  a  minimum  it  is  grouted  with  a  Portland  cement  grout  made 
of  one  part  cement  and  two  parts  sand.  This  grout  is  poured  upon  the  stone 
until  all  the  voids  are  filled  and  the  grout  flushes,  to  the  surface.  The  rolling 
is  continuous  during  the  process  of  grouting.  Upon  this  surface  is  placed 
a  very  thin  layer  of  pea  stone  which  is  spread  over  the  entire  area  of  the  road- 
way, grouted  and  rolled,  the  rolling  to  continue  until  the  grout  flushes  to  the 
surface.  Expansion  joints  are  left  along  the  curbs.  The  data  given  above  was 
taken  from  the  specifications  of  the  Hassam  Paving  Company  who  have  a 
patent  on  this  pavement. 

53 


Hassam  pavement  has  been  laid  upon  a  grade  of  7  per  cent  in  Biddeford, 
Maine. 

LONG  ISLAND   MOTOR  PARKWAY. 

The  automobile  is  rapidly  changing  the  conditions  governing  the  building 
of  improved  streets  and  highways.  This  is  particularly  noticeable  along  the 
suburban  highways  where  it  is  possible  to  run  automobiles  at  high  speeds. 
Concrete  pavement  seems  to  be  well  adapted  to  meet  the  conditions  imposed 
by  this  particular  class  of  traffic.  An  example  of  the  Hassam  type  of  pave- 


FIG.  IS.— CONSTRUCTION  OF  LONG  ISLAND  MOTOR  PARKWAY. 

ment  for  automobile  traffic  is  the  Long  Island  Motor  Parkway.  The  paved 
portion  of  this  parkway  is  several  miles  in  length  and  "ATLAS"  Portland 
Cement  was  used  throughout. 

The  method  of  construction  was  as  follows:  The  sub-grade  was  shaped 
and  rolled  with  a  lo-ton  roller.  A  2^-inch  layer  of  broken  stone  i%  to 
2%  inches  in  size  was  then  spread  upon  the  sub-grade  and  upon  this  broken 
stone  a  wire  fabric  reinforcement  was  laid  over  the  entire  width  of  the  road- 
way and  the  separate  sheets  overlapped  as  shown  in  the  photograph.  A  layer 


54 


of  broken  stone  was  then  spread  upon  the  fabric  so  as  to  conform  to  the  cross 
section  of  the  roadway  and  to  give  a  pavement  five  inches  in  thickness  after 
rolling. 


Concrete   \ 

33&\0<- 

\4CSQW/7 


tfc?/f  ^Section  /n  Cut  /-/&/f  ^Section  or>  /?// 


^e/n forced  Cortcrefe 


FIG.  20.— TYPICAL  CROSS  SECTION  OF  LONG  ISLAND  MOTOR  PARKWAY. 


After  the  ballast  was  placed  on  the  reinforcement  it  was  thoroughly  rolled 
and  compacted  with  a  ic-ton  roller.  Portland  cement  grout  made  with  one  part 
of  "ATLAS"  Portland  Cement  and  two  parts  sand  was  mixed  in  a  mechanical 
mixer  and  poured  upon  the  surface  of  the  rolled  ballast  until  all  the  voids  were 
filled  and  until  the  grout  flushed  to  the  surface  after  rolling.  The  grout  was 
colored  with  lampblack  to  slightly  darken  the  finished  pavement.  After  the 
grout  had  been  poured  and  rolled  a  thin  layer  of  pea  stone  was  spread,  grouted, 
and  the  surface  again  rolled  as  before. 

The  finished  pavement  was  given  a  rough  surface  by  brooming  so  as  to 
form  very  small  ridges  at  right  angles  to  the  length  of  the  roadway.  Care 
was  taken  to  complete  all  rolling  after  grouting  each  section  before  a  sufficient 
period  of  time  had  elapsed  to  allow  the  cement  to  take  its  initial  set.  Auto- 
mobiles were  allowed  on  the  finished  pavement  ten  days  after  completion. 

This  pavement  was  laid  by  the  Hassam  Paving  Company  of  Worcester, 
Mass.  No  provision  was  made  for  expansion  or  contraction,  but  as  previously 
stated  the  roadway  was  reinforced  with  wire  fabric.  Fig.  20  shows  typical 
sections  of  the  parkway.  The  upper  drawing  represents  construction  where 
the  road  is  straight,  and  the  lower  where  the  road  is  on  a  curve. 

55 


COST   OF  HASSAM   PAVEMENT. 

A  Hassam  pavement  was  completed  in  Watertown,  Mass.,  during  October, 
1908,  at  a  cost  of  $1.85  per  square  yard.  The  pavement  consists  of  a  6-inch 
thickness  of  rolled  broken  stone  grouted  with  one  part  "ATLAS"  Portland 
Cement  and  two  parts  clean,  fine,  sharp  sand.  The  grout  was  mixed  in  a 
Hassam  grout  mixer.  The  surface  of  broken  stone  after  the  first  grout  was 
placed  was  covered  with  a  pea  grade  of  broken  stone,  and  this  finer  stone  in 
turn  was  covered  with  a  grout  of  the  proportion  of  one  part  "ATLAS"  Port- 
land Cement  and  one  part  sand,  and  rolled  with  a  steam  road  roller  before  the 
first  grout  had  time  to  set. 


FIG.  21.— HASSAM  PAVEMENT,  WATERTOWN,  MASS. 


HASSAM    GRANITE    BLOCK    PAVEMENT. 

River  Street,  in  Troy,  N.  Y.,  is  paved  with  a  Hassam  Granite  Block  Pave- 
ment on  a  Hassam  foundation.  The  foundation  in  this  pavement  consists  of 
a  6-inch  layer  of  broken  stone  grouted  with  one  part  "ATLAS"  Portland 
Cement  and  four  parts  sand.  Grout  was  mixed  in  a  Hassam  grout  mixer,  was 
poured  upon  the  broken  stone  until  all  voids  were  filled  and  the  grout  flushed 

56 


to  surface.  This  foundation  was  rolled  during  the  process  of  grouting  as 
well  as  being  thoroughly  compacted  by  rolling  before  the  grout  was  applied. 

The  pavement  proper  consists  of  granite  paving  blocks  having  dimensions 
4  to  4^/2  inches  deep,  3%  to  4^2  inches  wide  and  6  to  12  inches  long,  laid  on 
edge  across  the  street  on  a  sand  cushion  i%  inches  in  thickness  placed  on  the 
Hassam  foundation.  Pea  stone  was  sprinkled  upon  the  surface  of  the  blocks 
and  swept  into  the  joints  with  wire  brooms,  the  pavement  rolled  to  an  even 
surface  or  rammed  when  roller  could  not  be  used,  and  the  surface  was  then 
swept  clean  and  the  joints  filled  with  a  grout  made  of  one  part  "ATLAS" 
Portland  Cement  and  one  part  clean,  sharp  sand.  The  grout  was  spread 
upon  the  paving  and  brushed  into  the  joints,  the  stone  blocks  having  pre- 
viously been  wet  by  sprinkling,  and  the  grout  was  then  broomed  to  a  fine 
smooth  surface.  The  blocks  were  laid  with  joints  not  to  exceed  ^  inch. 

The  sand  cost  $1.25  per  cubic  yard  delivered  upon  the  street  in  bags. 
Crushed  stone  cost  $1.45  per  cubic  yard  delivered.  Day  labor  cost  $1.75  per 
day  of  8  hours.  Contract  price  including  all  materials  and  labor  was  $3  per 
square  yard.  Fig.  22  shows  a  cross  section  of  this  street. 


k 


foundation,  Concrete  6 

vo/ds  f/7/ed  wttf>  grouf  of 


//*?//  Af/0s  Cemenf  and 

•4  paste  of  *sand.  ^/jou/der  of  Cur 6  £' 

Crow/?  of  *5freef  'f'onSS&O*    ^/dewa/fr  *s/o&e  £' per  foot 

FIG.  22.— CROSS  SECTION    OF  GRANITE  BLOCK  PAVEMENT  ON  RIVER  STREET,  TROY,  N.  Y. 

CONCRETE  PAVEMENT  IN  RICHMOND,  IND. 

Numerous  streets  and  alleys  have  been  paved  with  concrete  in  Richmond 
as  previously  stated  in  this  chapter.  The  first  concrete  street  pavement  in 
Richmond  was  laid  in  1896  at  a  cost  of  $1.62  per  square  yard,  since  then  the 
cost  has  been  still  further  reduced. 

The  usual  pavements  for  streets  of  ordinary  traffic  in  Richmond  have  a 
concrete  base  5  or  6  inches  thick  with  a  top  wearing  surface  i  or  i*4  inches 
thick. 


57 


For  such  pavements,  that  is,  those  requiring  a  thickness  of  6  or  7  inches, 
a  foundation  consisting  of  8  inches  of  rubble,  field  cobble  stone,  the  refuse 
from  quarries,  or  coarse  gravel  is  placed.  On  this  layer  is  spread  sufficient 
gravel  to  fill  the.  spaces,  and,  after  flooding  and  ramming,  to  make  a  total 
thickness  of  the  foundation  of  10  inches. 

On  this  foundation  5  inches  of  thoroughly  rammed  1 12 15  concrete  is  laid  in 
blocks  10  feet  by  15  feet. 

The  wearing  surface,  1^2  inches  in  thickness,  and  composed  of  one  part 
cement  and  two  parts  clean,  coarse  sand;  or  else  of  one  part  cement,  one  part 
sand,  and  one  part  clean,  crushed  stone  screenings,  must  be  placed  on  the 
5-inch  base  before  the  latter  has  set.  This  wearing  surface  is  troweled  down 
to  insure  contact,  then  leveled  off  with  a  straight  edge.  When  hard  enough 
it  is  floated  or  troweled  to  a  smooth,  continuous  surface. 

The  surface  is  finally  pitted  with  a  brass  roller  except  for  marginal  strips 
two  inches  wide  around  the  edges  of  the  blocks.  The  wearing  surface  is  cut 
into  blocks  the  same  size  as  the  base. 

For  streets  having  heavy  traffic  a  concrete  base  is  laid  in  addition  to  the 
regular  pavement  so  that  the  total  thickness  is  the  same  as  a  brick  pavement 
on  a  concrete  foundation  or  about  eleven  inches  total.  These  pavements  are 
constructed  as  follows: 

Where  necessary  an  8-inch  layer  of  gravel  thoroughly  wet  and  consolidated 
is  used  for  sub-drainage  and  upon  this  gravel  foundation  is  placed  a  6-inch 
layer  of  1 13 :6  Portland  cement  concrete.  When  this  concrete  foundation  is 
strong  enough  to  sustain  the  roadway  pavement  it  is  covered  with  a  coating 
of  fine  sand,  raked  off  with  a  flat  board  rake  so  as  to  remove  all  sand  except 
that  which  may  remain  in  low  places  and  voids  in  the  concrete  foundation. 
Upon  this  sand  is  placed  a  thin  layer  of  tar  paper  and  upon  the  paper  a  1 12 :5 
concrete  layer  four  inches  thick. 

Upon  the  above  concrete  is  placed  a  wearing  surface  one  inch  in  thickness 
composed  of  one  part  cement,  one  part  clean,  sharp  sand,  and  one  part  clean 
stone  or  granite  screenings,  mixed  with  water  to  form  a  rather  wet  facing 
mixture.  In  some  cases  this  wearing  surface  is  placed  in  two  layers,  each 
one-half  inch  thick,  the  first  to  be  thoroughly  rammed  to  insure  perfect  con- 
tact; the  second  applied  immediately  after  and  troweled  and  worked  over, 
and  made  to  conform  to  the  finished  surface  of  the  street.  When  sufficiently 
hard,  the  surface  is  floated  and  steel  troweled  and  finished  with  a  cork  float. 

CONCRETE  PAVEMENTS  IN  THE  CITY  OF  PANAMA. 

Fig.  23  shows  West  Fifteenth  Street  in  the  city  of  Panama  being  paved 
with  1:25/2:5  "ATLAS"  cement  concrete  five  inches  thick;  after  tamping  in 
place  it  is  finished  with  a  straight  edge  and  trowel.  The  surface  is  smooth  but 

58 


not  slippery.  The  concrete,  hand  mixed,  was  placed  with  wheelbarrows. 
Broken  stone  was  obtained  by  crushing  old  cobble  stones.  The  sand  was  ob- 
tained from  Panama  Beach.  In  1906  and  1907  over  two  miles  of  this  pavement 
was  laid  in  the  city  of  Panama  at  a  cost  of  $2  per  square  yard  on  streets  having 
grades  as  high  as  8  per  cent.  It  was  laid  in  alternate  blocks  or  sections  about 
10  feet  long  lengthwise  of  the  street  and  extending  all  of  the  way  or  one-half 
way  across  the  street  between  curbs.  The  streets  vary  in  width  from  13  feet 
to  20  feet  between  curb  lines. 


FIG.  23.— CONCRETE  PAVEMENT  IN  THE  CITY  OF  PANAMA. 

GROUTING  STONE  BLOCK  AND  BRICK  PAVEMENTS. 

For  filling  the  joints  in  stone  block  or  brick  pavements  the  cement  grout 
should  be  mixed  one  part  "ATLAS"  Portland  Cement  and  one  part  clean  sand 
with  enough  water  to  make  the  grout  flow  easily.  The  materials  must  be 
thoroughly  mixed  with  hoes  in  a  tight  box  at  the  place  of  using.  As  soon  as 
the  mixing  is  completed  the  grout  must  be  immediately  poured  out  of  the  box 
upon  the  surface  of  the  pavement  and  broomed  into  the  joints  before  the 
cement  sets. 

Every  twenty-five  feet,  measured  lengthwise  of  the  street,  one  or  two 
transverse  joints  should  be  filled  with  tar  to  provide  for  expansion.  The  joint 
next  to  each  curb  should  also  be  filled  with  tar. 

59 


CHAPTER    IV. 

SEWERS,  DRAIN  TILES,  BROOK  LININGS,  CONDUITS. 

SEWERS. 

While  formerly  all  large  sewers  were  built  of  brick  and  the  smaller  ones  of 
vitrified  clay  or  cast-iron  pipe,  in  recent  years  concrete  has  entered  this  field 
of  construction  and  through  a  process  of  expansion  and  adaptation  has  been 


BOX  CULVERT,  AMHERST,  MASS. 

gradually  supplanting  all  of  these  materials.  At  first  its  use  was  limited  to 
foundations  and  the  lower  part  of  side  walls,  then  to  lining  the  inverts  of  brick 
sewers,  and  finally  increasing  experience  and  additional  confidence  has  led  to 
its  use  for  the  construction  of  entire  concrete  sewers  and  also  sewer  pipes. 

The  larger  concrete  sewers,  molded  in  place,  are  practically  monolithic, 
while  the  smaller  ones,  constructed  by  joining  short  lengths  of  concrete  pipes 
together  and  sealing  the  joints,  make  one  continuous  pipe. 

Aside  from  being  generally  cheaper  than  brick,  concrete  sewers  are  more 
permanent  and  water-tight,  have  a  much  smoother  surface  and  therefore  a 
greater  carrying  capacity,  and  are  less  liable  to  damage  and  collapse  through 
excessive  loads,  vibrations  and  unsuitable  foundations. 

60 


CONCRETE  PIPE  SEWERS. 

While  monolithic  sewers  molded  in  place  are  entirely  satisfactory  for  diam- 
eters of  more  than  30  inches,  owing  to  the  difficulty  of  devising  suitable  forms 
they  are  impractical  and  less  economical  for  smaller  diameters.  Concrete 
pipe,  on  the  other  hand,  can  be  made  economically  and  easily  in  sizes  ranging 
from  3  inches  to  36  inches  inside  diameter. 

Concrete  pipes  can  be  made  wherever  gravel,  sand  and  cement  can  be 
brought  together,  and  at  a  cost  considerably  lower  than  cast-iron  pipe  and 
usually  less  than  vitrified  clay.  They  can  be  molded  as  desired  into  sectional 
forms  which  are  more  conducive  to  stability  and  efficiency  than  the  circular 
cross-section  which  is  necessary  with  cast  iron  or  vitrified  clay.  By  giving 
concrete  pipe  a  broad,  flat  level  base,  they  are  made  to  rest  firmly  and  securely 
on  a  continuous,  flat  earth  foundation,  while  to  secure  such  a  bearing  for  a 
circular  pipe  requires  tamping  the  earth  filling  into  the  space  beneath  the  two 
sides  of  the  pipe  and  also  cutting  out  a  depression  in  which  the  bells  can  rest. 

In  localities  where  there  are  great  variations  in  the  amount  of  sewage 
flowing  through  the  pipes  an  oval  form  of  cross  section  is  better  than  a  cir- 
cular one.  For  this  concrete  must  be  used,  since  vitrified  pipe  cannot  be  made 
into  these  forms  on  account  of  the  warping  due  to  burning. 

This  warping  also  prevents  the  finished  section  of  vitrified  pipe  from  being 
truly  circular  so  that  when  these  pipes  are  fitted  together  there  are  rough 
projections  at  many  points  on  the  inside  of  the  pipe  which  tend  to  collect 
solid  matter  in  the  sewage  and  thus  to  reduce  its  carrying  capacity. 

Concrete  pipes  can  be  given  a  tapering  butt  joint,  instead  of  the  bell  and 
spigot  joint  common  for  vitrified  and  cast-iron  pipe,  which  considerably  re- 

TESTS  OF  PLAIN  CONCRETE  SEWER  PIPE  IN  BROOKLYN.* 


Kind 

Diameter, 
Inches 

Thickness, 
Inches 

Age 

Breaking 
Load,  Lb. 
per  Lin.  Ft. 

A 

12 

13/16 

32  days 

1,689 

B 

15 

17/16 

33  days 

1,800 

B 

18 

1% 

.  .  29  days 

1,767 

A 

12 

1%6 

.  1  month  .... 

.  .  29  days 

1,622 

B 
B 
C 

15 
18 
6 

IH 

17/16 
15/16 



.  2  months  .  .  . 
.  1  month  .... 

.  .   3  days 
.  .  29  days 

1,617 
1,522 
2,600 

A 

9 

13/16 

Several 

years  over  3 

years 

2,011 

A 

12 

1±4 

2  years 

9  days 

1.983 

B 

15 

ll/o 

1  year 

7  months 

20  days 

1,962 

B 

18 

1% 

2  years 

.  .   7  days 

2,022 

B 

24 

2% 

2  years  .... 

.  1  month  .... 

.  .  28  days 

1,978 

A,  circular  pipe  with  flat  base.     B,  egg-shape  with  flat  base.     C,  circular  pipe. 


*Part  of  table  from  Engineering  Record,  Vol.  58,  Nov.  21,  1908,  p.  591. 

61 


duces  both  the  cost  of  manufacture  and  of  joining  the  pipe  with  mortar  in 
the  trench. 

That  concrete  pipes  without  reinforcement  possess  sufficient  strength  for 
use  as  sewers  is  shown  in  the  accompanying  table*  which  gives  the  results  of 
tests  on  pipes  made  in  the  testing  laboratory  of  the  Bureau  of  Sewers  of 
Brooklyn,  N.  Y. 

The  pipes  which,  as  seen  from  the  accompanying  table,  varied  in  diameter 
from  6  to  24  inches,  were  made  of  a  mixture  of  i*/2  parts  cement  to  i  part 
sand  to  3  parts  trap  rock  screenings,  and  were  tested  at  ages  varying  from 
twenty-nine  days  to  over  two  years.  The  6-inch  pipes  were  made  24  inches 
long  while  the  larger  diameters  were  36  inches  in  length.  They  were  tamped 
into  molds,  and  then  subjected  to  heat  to  dry  them  immediately  after  molding, 


m> 


CULVERT,  DUMONT,  N.  J. 


the  forms  being  removed  within  half  an  hour  after  the  work  on  a  length  was 
started. 

In  testing  a  section  of  the  pipe  it  was  laid  on  a  sand  bed  so  that  the  lower 
one-sixth  of  its  circumference  was  in  contact  with  the  sand  and  then  the 
pressure  was  applied  from  the  testing  machine  along  the  upper  surface  of  the 
pipe  until  the  pipe  broke.  In  order  to  secure  an  even  distribution  of  the 
pressure  along  the  length  of  the  pipe,  the  pressure  was  applied  through  a  strip 
of  plaster  of  Paris  one  inch  wide  and  not  over  one-quarter  inch  thick,  held  in 
place  by  strips  of  wood. 

62 


The  accompanying  table  shows  the  sizes  of  the  pipe  in  inches  together 
with  the  thickness  of  the  walls,  the  age,  and  the  breaking  load  in  pounds  per 
linear  foot.  In  order  to  break  a  1 2-inch  pipe  32  days  old,  for  example,  a  load 
of  1,689  pounds  on  each  foot  of  length  of  the  pipe  was  required,  the  total  load 
for  the  3  feet  of  pipe  being  thus  three  times  1,689,  °r  5»°67  pounds. 

The  pipes,  it  must  be  remembered,  were  of  plain  concrete  without  rein- 
forcement. 

LARGE   CONCRETE   SEWERS. 

Large  sewers  and  conduits  are  built  of  plain  concrete  and  also  of  reinforced 
concrete.  For  diameters  of  3  to  4  feet  the  thickness  required  for  good  con- 
struction is  usually  sufficient  without  reinforcement  as  they  can  be  reckoned 
as  strong  as  a  brick  sewer  of  the  same  diameter  which  is  half  again  as  thick. 
For  large  diameter,  reinforcement  is  generally  advisable,  and  the  saving  in 
material  will  more  than  counterbalance  the  added  cost  of  reinforcing.  The 
reinforcement  adds  to  the  strength  of  the  sewer  during  construction,  and  when 
completed  enables  it  to  withstand  a  larger  pressure  after  the  earth  is  filled 
in  around  and  on  top  of  the  pipe,  and  also  renders  it  less  liable  to  damage 
where  there  is  danger  of  settlement. 

THICKNESS  OF  CONDUITS* 


Diameter  of 
Conduit 

Thickness  of 
Crown,  Inches 

Thickness  of 
Haunch,  Inches 

Thickness  of 
Invert,  Inches 

2 
6 
12 

4 
7 
13 

6 
18 
23 

5 
8 
14 

"If  reinforcement  is  used,  the  thickness  for  conduits  for  ordinary  sizes  is  usually  determined  by  the  minimum 
thickness  of  concrete  which  can  be  laid  so  as  to  properly  imbed  the  metal.  This  minimum  for  the  large  diameters 
where  steel  is  advisable  may  be  taken  as  6  inches." 

As  a  guide  for  determining  the  thickness  of  concrete  required  for  both 
plain  and  reinforced  concrete  sewers,  the  general  rule  used  by  Mr.  William  B. 
Fuller*  is  given  as  follows: 

"If  concrete  is  not  reinforced  and  ground  is  good — able  to  stand  without  sheeting- 
make  crown  thickness  a  minimum  of  4  inches,  and  then  one  inch  thicker  than  diameter 
of  sewer  in  feet.  Make  thickness  of  invert  same  as  crown  plus  one  inch  except  never 
less  than  5  inches..  Make  thickness  at  haunches  two  and  a  half  times  thickness  of 
crown,  but  never  less  than  6  inches..  If  ground  is  soft  or  trench  is  unusually  deep, 
these  thicknesses  must  be  increased  according  to  experienced  judgment." 

SIZES  OF  CIRCULAR  CONCRETE  SEWER  PIPE. 
Fig.  24  shows  one  form  of  concrete  circular  pipes  suitable  for  sewer  con- 


*See  reference,  footnote,  page  18. 


struction.  The  pipes  are  shown  2  feet  6  inches  in  length  over  all,  the  inside 
diameters  can  be  anything  from  12  to  48  inches,  and  the  thickness  of  the  pipe 
from  2  to  6  inches.  The  joints  are  beveled  so  that  when  laid  with  Portland 
cement  mortar  the  joints  will  be  practically  water  tight,  and  will  present  a 
smooth  surface  so  that  solid  matter  will  not  be  deposited,  as  is  apt  to  be  the 
case  in  vitrified  pipe  sewers. 

In  laying  these  pipes  a  little  mortar  mixed  i  part  "ATLAS"  Portland 
cement  and  2  parts  clean  sharp  sand  is  placed  inside  of  the  pipe  in  the  inner 
beveled  surface.  The  pipe  is  then  pushed  hard  against  the  beveled  end  of  the 
length  of  pipe  already  laid,  and  the  mortar  smoothed  off  inside  and  outside  of 
the  pipe  so  as  to  make  a  smooth  joint. 


FIG.  24.— LONGITUDINAL  SECTION  OF  SEWER  PIPES. 

The  inside  diameter  of  the  pipes,  D  in  Fig.  24,  are  12,  18,  24,  30,  36,  42, 
and  48  inches,  and  the  thickness  T  in  the  figure  corresponding  to  these  dia- 
meters should  be  2,  3,  4^4,  4^,  434,  534,  and  6  inches.  That  is,  for  a  1 2-inch 
pipe  the  thickness  should  be  2  inches;  for  an  1 8-inch  pipe,  3  inches,  and  so  on. 
For  drain  tile,  which  need  not  be  so  thick  as  sewer  pipe,  thinner  pipe  may  be 
used. 


PROPORTIONS  OF  CONCRETE  FOR  SEWER  PIPE. 

Concrete  used  in  the  construction  of  sewer  pipe,  that  is,  in  the  construction 
of  pipes  having  diameters  of  12  or  more  inches,  should  be  mixed  in  the  propor- 
tions of  i  part  "ATLAS"  Portland  Cement,  2  parts  clean,  sharp  sand,  to 
4  parts  crushed  stone  or  clean  coarse  gravel  not  more  than  i  inch  in  diameter. 

64 


CONCRETE  DRAIN  TILE.* 

Tiles  are  used  for  draining  roadways  and  farms.*  A  roadway  of  even  the 
best  material  needs  some  drainage  and  for  roadways  made  of  poor  materials 
drainage  is  absolutely  essential.  Concrete  drain  tiles  are  the  best  for  the  under 
drainage  of  any  roadway  or  sidewalk.  Oftentimes  in  the  construction  of  roads 
and  sidewalks  one  or  more  longitudinal  lines  of  drain  pipes  are  laid  underneath 
the  surface  of  the  road  or  sidewalk  and  at  convenient  places  are  carried  to 
proper  outlets.  Frequently  a  drain  4  inches  in  diameter  is  sufficient  for  drain- 
ing sidewalks  or  roadways. 

SIZE  OF  CONCRETE  DRAIN  TILES. 

Concrete  drain  tiles  are  made  in  sizes  of  4  inches  to  30  inches  inside  dia- 
meter. Ordinarily  the  sizes  from  4  to  12  inches  are  molded  by  machine,  al- 
though they  may  be  made  in  simply  constructed  molds  as  described  in  "Con- 
crete Construction  about  the  Home  and  on  the  Farm,"  while  the  larger  sizes 
are  usually  made  by  hand.  Although  concrete  sewer  pipes  have  either  bell 
shaped  or  other  similar  joints,  concrete  drain  tiles  are  nearly  always  made 
with  plain  ends. 

The  thickness  of  the  shell  for  tiles  varies  from  i  inch  or  even  thinner  for 
the  4-inch  pipes  to  3  inches  for  the  36-inch  pipes.  The  sizes  under  10  inches 
in  diameter  are  made  i  inch  or  less  in  thickness;  the  12  to  24-inch,  from  i  to  2 
inches  thick ;  the  24  to  36-inch,  3  inches. 

Usually  sizes  under  10  inches  in  diameter  are  made  18  inches  long  and  those 
10  inches  or  more  are  made  2  feet  long. 

MIXTURES  FOR  TILES. 

The  best  mixture  for  tiles  is  i  part  "ATLAS"  Portland  Cement  to  3  parts 
clean  coarse  sand,  or  sand  and  gravel  passing  a  ^2-inch  screen. 

A  1 13  mixture  for  drain  tiles  to  be  used  in  roads,  either  for  longitudinal  or 
cross  drains,  gives  the  proper  strength  to  the  pipes.  For  farm  drainage  and 
other  similar  locations  where  there  is  not  much  pressure  exerted  upon  the  pipe 
a  1 14  mixture  is  sometimes  used. 

CURING. 

For  ordinary  drain  tiles  the  concrete  should  be  mixed  with  enough  water 
so  that  the  moisture  will  show  at  the  surface  when  the  concrete  is  tamped.  As 
a  general  thing,  the  molds  can  be  removed  as  soon  as  the  concrete  is  thor- 


*See  also  "Concrete  Construction  about  the  Home  and  on  the  Farm,"  p.  91.    This 
book  may  be  obtained  by  writing  to  The  Atlas  Portland  Cement  Co.,  New  York. 

65 


oughly  rammed  into  them.  After  the  molds  are  removed,  the  tiles  should  be 
placed  in  the  shade,  and  wet  down  as  soon  as  the  concrete  will  stand  the  water 
without  washing,  which  is  ordinarily  from  8  to  10  hours  after  molding.  It  is 
of  the  utmost  importance  that  they  should  not  be  allowed  to  dry  out  for  at 
least  4  days,  and  they  should  also  be  kept  in  the  shade  for  8  or  10  days,  being 
wet  once  or  twice  each  day  during  this  period.  If  the  weather  is  very  dry  or 
hot,  3  or  4  wettings  for  the  first  few  days  are  desirable.  A  pretty  good  rule  to 
follow  is  that  the  pipes  must  not  be  allowed  to  dry  "white"  until  they  are  at 
least  8  days  old.  After  this  treatment  the  tiles  should  be  stored  in  an  open 


FIG.  25.— CONCRETE  BROOK  LINING  IN  NEWTON,  MASS. 

yard  to  season  and  harden.    In  ordinary  weather  the  pipes  are  ready  for  ship- 
ment in  30  days. 

LAYING  DRAIN  TILES. 

Concrete  drain  tiles  under  roads  must  have  at  least  i  foot  of  earth  on  the 
top  of  the  pipe  and  they  must  be  laid  on  a  grade  of  at  least  i  foot  in  100  feet, 
that  is,  one  foot  fall  of  the  pipe  in  100  feet  of  distance. 

The  pipes  should  be  laid  with  open  joints,  that  is,  with  the  ends  simply 
abutting  without  any  mortar. 

66 


BROOK   LININGS. 

A  small  stream  of  water  running  through  a  town  or  through  the  flats  ad- 
joining a  town  often  is  the  cause  of  a  great  deal  of  trouble.  If  the  adjoining 
lands  are  to  be  divided  into  house  lots  the  brook  must  be  properly  taken  care 
of.  Usually  the  best  solution  for  this  problem  is  to  change  the  course  of 
the  brook  so  that  it  will  flow  under  a  street  through  a  concrete  conduit.  If 
the  stream  is  not  within  the  limits  of  a  street  the  banks  can  be  lined  with 


END  ELEMT/ON 


rods  spaced /O." 


d-A. 


FIG.  26.— CONCRETE  BROOK  LINING  IN  NEWTON,  MASS. 

concrete,  the  top  thus  being  left  open.  The  concrete  lining  prevents  the 
nuisance  caused  by  the  breeding  of  mosquitoes  and  other  insects  along  the 
edges  of  the  open  brook.  Fig.  26  shows  typical  drawings  of  a  brook  lining  in 
Newton,  Massachusetts.  The  concrete  lining,  throughout  most  of  the  length 
is  curved  to  a  radius  of  18  inches,  inside  diameter,  and  for  the  most  part  is 
8  inches  in  thickness,  the  invert  being  8  inches  and  the  thickness  at  the  upper 

67 


surface  of  the  concrete  being  14  inches.  Under  the  ordinary  flow  the  concrete 
channel  does  not  run  full.  During  extreme  high  water  the  cross  section  of 
the  channel  is  not  sufficient  to  carry  the  entire  flow  so  that  once  in  a  great 
while  the  water  overflows  the  normal  cross  section. 

Fig.  26  shows,  in  addition  to  the  normal  cross  section  of  the  channel,  the 
sections  where  it  enlarges  to  pass  under  a  small  culvert  which  carries  a  street 
over  the  brook.  At  section  A-A  the  concrete  is  reinforced  with  half-inch  rods 
spaced  10  inches  apart.  The  culvert  itself  has  a  clear  span  of  8  feet  and  a 
total  depth  of  5  feet.  The  thickness  of  the  invert  of  the  culvert  is  6  inches  at 
the  middle,  gradually  enlarging  towards  the  abutments  while  the  arch  is  7 
inches  thick  at  the  crown  and  increases  gradually  towards  the  abutments  and 
is  reinforced  with  j4-inch  steel  rods  8  inches  apart  on  centers. 


Concrete 


£' fw/sfa/ Jrix/ 

2&O" apart 
j/ee/ 

/2"  apart 


J&C//0/7    //? 

FIG.  27.—  TYPICAL  CROSS  SECTION,  JERSEY  CITY  CONDUIT, 


The 


Fig.  25  is  an  illustration  of  the  brook  shown  in  detail  in  Fig.  26. 
photograph  was  taken  at  a  very  low  stage  of  the  water. 

For  brook  linings  the  concrete  should  be  mixed  i  part  "ATLAS"  Portland 
Cement,  2^  parts  sand  and  5  parts  broken  stone  or  screened  gravel.  Concrete 
linings  should  be  laid  in  sections  not  over  20  feet  in  length,  and  the  end  of 
one  section  should  be  built  into  the  adjacent  section  in  a  tongued  and  grooved 
manner. 

Sometimes  these  concrete  brook  linings  are  connected  with  nearby  sewers 

68 


so  that  the  sewers  are  automatically  or  continuously  flushed  by  some  water 
passing  from  the  brook  into  the  sewer. 

CONDUITS. 

Oftentimes  a  covered  conduit  is  necessary  to  carry  the  water  of  a  brook 
located  under  a  street  surface.  Such  conduits  may  be  made  rectangular  or 
circular  in  cross  section.  They  are  also  frequently  used  for  water  supply 
lines  where  there  is  little  or  no  pressure  within  the  concrete  conduit. 


FIG.  28— JERSEY  CITY  CONDUIT. 

Fig.  27  shows  a  typical  cross  section  and  Fig.  28  a  photograph  of  a  con- 
crete conduit  of  the  Jersey  City  Water  Supply  Company  built  to  carry  a  water 
supply.  This  conduit  is  approximately  8  feet  6  inches  inside  diameter  and  for 
a  length  of  about  20,000  feet  is  made  of  concrete.  About  30,000  barrels  of 
"ATLAS"  Portland  Cement  were  used  in  this  conduit. 

The  thickness  of  the  conduit  at  the  crown  varies  from  5  to  8  inches  de- 
pending on  the  kind  of  material  in  which  the  pipe  is  placed  and  the  depth  of 
the  filling  over  the  pipe.  The  section  shown  in  Fig.  27  is  typical  of  those  used 
in  soft  earth. 

For  sections  laid  in  open  trench  the  concrete  was  mixed  i  part  "ATLAS" 
Portland  Cement  and  7  parts  sand  and  ballast.  The  ballast  was  broken  trap 
rock,  the  run  of  the  crusher  being  used.  All  concrete  was  machine  mixed 
and  was  very  wet. 

69 


CHAPTER  V. 

CULVERTS. 

Concrete  is  an  excellent  material  for  the  construction  of  culverts  as  is 
shown  by  the  great  number  of  concrete  culverts  now  being  built  for  highways 
and  railways.  As  the  entire  culvert  is  made  of  concrete  there  is  nothing  to 
decay  and  the  excessive  maintenance  charges  in  timber  construction  are  en- 
tirely lacking. 

Culverts  vary  greatly  in  size  and  shape.     The  best  way  to  determine  the 


BEAM  BRIDGE  NEAR  PARIS,  MO. 

required  size  for  an  opening  so  that  the  waterway  will  be  sufficient  is  to 
measure  the  width  and  depth  of  the  stream  at  some  narrow  point  near  by 
during  the  high  water  stage,  and  if  possible  compare  this  size  with  that  of 
culverts  over  the  same  stream  in  the  neighborhood.  With  this  information 
the  width  and  depth  of  the  culvert  opening  may  be  chosen. 

Culverts  may  be  either  square,  rectangular,  circular,  or  arched  in  cross 
section.  Generally  the  rectangular  section  is  best  because  it  conforms  more 
nearly  to  the  cross  section  of  the  water  way  and  is  cheaply  and  easily  built. 
Where  the  appearance  is  of  more  importance  than  the  cost,  arch  culverts  are 
preferable  to  other  styles.  Whatever  the  form  of  cross  section  the  construc- 

70 


1 


Fbrf  P/an 


6rOOrBOX  Ci/LVERT 

FIG.  29.— REINFORCED  CONCRETE  BOX  CULVERTS. 


72 


tion  should  be  such  as  to  prevent  undermining,  that  is,  to  prevent  the  water 
from  running  along  the  outside  of  the  culvert  and  thus  washing  out  the  earth 
embankment. 

Culverts  with  square  or  rectangular  openings  are  called  box  culverts,  and 
those  with  circular  sections  are  called  pipe  or  circular  culverts.  Pipe  culverts 
are  made  entirely  of  concrete  or  else  of  tile  or  iron  pipe  with  a  concrete  head 
wall  at  each  end  of  the  pipe  where  it  projects  from  the  sides  of  the  road. 


BEAM  BRIDGE. 

Concrete  for  culverts  should  be  made  one  part  "ATLAS"  Portland  Cement, 
two  and  a  half  parts  sand,  and  five  parts  broken  stone. 

BOX    CULVERTS. 

Box  culverts  may  have  square  or  rectangular  sections  as  in  Fig.  29  or; 
Fig.  32  or  a  section  similar  to  that  shown  in  Fig.  30.  For  small  culverts,  the 
last  is  a  neat  design,  having  an  arch  effect  and  yet  being  cheaply  and  easily 
constructed.  The  cost  of  the  small  box  culvert  shown  in  Fig.  30  may  be. 
slightly  reduced  if  the  cross  section  is  made  square,  omitting  the  bevels  at  the 
upper  corners. 

Fig.  29  shows  a  good  design  for  a  4-foot  box  culvert  of  ample  strength  to 
carry  a  highway..  To  prevent  undermining,  a  concrete  invert  or  bottom  is 
used  and  a  baffle  wall  and  apron  at  each  end  should  be  constructed  as  shown 

73 


although  some  culverts  where  the  soil  is  hard  do  not  need  the  apron,  baffle 
wall  or  bottom.  Cobble  stones  or  paving  bricks  may  be  used  instead  of 
concrete  for  covering  the  bottom  between  the  side  walls.  They  may  be  laid 
even  in  running  water  and  in  case  a  dry  season  should  occur  the  spaces  be- 
tween the  stones  or  bricks  may  be  filled  with  cement  grout.  Concrete  must 
not  be  laid  in  running  water  for  the  cement  will  be  washed  out  from  the 
aggregate.  This  4-foot  box  culvert  has  top,  bottom  and  sides  8  inches  in 
thickness  and  is  reinforced  with  expanded  metal  No.  10  gage  having  3-inch 
meshes,  or  with  other  similar  reinforcement  placed  not  less  than  iJ/2  and  not 
more  than  2  inches  from  the  inner  surface  of  the  culvert.  The  sheet  rein- 
forcement should  also  be  placed  in  the  apron  and  in  the  wing  walls. 

The  lower  part  of  Fig.  29  shows  a  design  for  a  box  culvert  with  opening 
6  by  6  feet  similar  to  the  4-foot  box  culvert  above  described  except  that  round 
steel  rods  are  used  instead  of  sheet  reinforcement.  In  the  bottom  of  the  cul- 
vert proper  the  rods  running  at  right  angles  to  the  length  of  the  culvert  should 
be  54  inch  in  diameter  and  spaced  5  inches  apart.  For  the  top  they  should 
be  5/s  inch  in  diameter,  spaced  5  inches  apart  and  alternate  rods  should  be 
bent,  as  shown  in  Fig.  29,  to  reinforce  the  side  walls  extending  within  three 
inches  of  the  bottom  surface  of  the  concrete.  This  bending  of  the  alternate 
rods  in  the  top  results  in  the  vertical  rods  of  the  sides  being  spaced  10  inches 
apart.  In  the  apron  the  s^-inch  rods  should  be  spaced  5  inches  apart  and! 
should  be  bent  up  alternately  so  that  the  vertical  rods  in  the  wing  walls  are 
spaced  10  inches. 

In  addition  to  the  rods  above  mentioned  there  should  be  a  set  of  ^-inch 
diameter  rods  running  parallel  to  the  length  of  the  culvert  spaced  10  inches 
apart  which  should  extend  into  the  apron  and  wing  walls  at  each  end. 

Fig.  31  and  Fig.  32  show  a  reinforced  box  culvert  built  in  Lenox,  Massa- 
chusetts, in  1896,  for  the  Massachusetts  Highway  Commission.  The  body  of 
the  culvert  is  reinforced  with  %-inch  square  twisted  steel  rods  8  inches  c.  to  c. 
at  each  corner  where  the  side  walls  meet  the  top  and  bottom,  those  at  the 
bottom  corners  being  24  inches  long  and  bent,  while  those  at  the  top  corners 
are  straight  and  14  inches  in  length.  Four  counterforts  for  bracing  the  side 
walls  are  shown  in  the  plan  and  also  in  section  CiC,  Fig.  32,  are  used  in  this 
culvert. 

Forty  cubic  yards  of  broken  stone,  16  cubic  yards  of  sand,  55  barrels  of 
cement,  and  778  pounds  of  steel  were  used.  One  hundred  twenty-one  cubic 
yards  of  earth  were  excavated.  The  concrete  mixture  was  about  one  part 
"ATLAS"  Portland  Cement,  two  and  one-half  parts  sand,  and  five  parts 
crushed  stone,  and  the  44  cubic  yards  in  the  structure  cost  $660,  or  $15  per 
cubic  yard.  The  earth  excavation  cost  75  cents  per  cubic  yard.  The  total  cost 
of  the  culvert  to  the  Commission,  exclusive  of  the  macadam  roadway  was 

74 


$809.67.  The  cement  cost  the  contractor  $1.85  per  barrel,  plus  50  cents  for 
hauling,  making  the  price  at  the  culvert  $2.35  per  barrel.  The  contractor  paid 
$2  per  load  of  about  i  cubic  yard  for  the  sand  delivered  at  the  culvert  and* 
about  $1.15  per  cubic  yard  for  the  stone.  About  3*4  or  4  days  were  required 
for  excavating  and  the  concreting  extended  over  24  days  including  delays.  * 
A  small  box  culvert  with  an  opening  2  by  2  feet  is  shown  in  Fig.  30  in 
which  the  head  wall,  culvert  proper,  and  arrangement  of  forms  are  all  clearly 
illustrated.  If  the  soil  is  compact  material  like  hard  clay,  where  the  excava- 
tion can  be  made  to  the  exact  size  and  shape  of  the  culvert,  the  outer  forms 
may  be  omitted,  the  concrete  being  deposited  directly  on  the  bottom  of  the 


FIG.  31.— REINFORCED  CONCRETE  BOX  CULVERT  AT  LENOX,  MASSACHUSETTS. 

trench  to  form  the  invert  of  the  culvert,  then  the  inner  form  set  in  place  and 
the  concrete  deposited  between  it  and  the  walls  of  the  trench. 

The  inner  forms  consist  of  frames  made  of  three  pieces  of  2  by  4  inch  and 
one  piece  of  2  by  6-inch  joists,  notched  as  shown.  Around  these  frames  boards 
are  set.  The  upper  2  by  6  piece  is  not  nailed  so  that  in  removing  the  inner 
forms  after  the  concrete  has  hardened  this  upper  piece  is  first  knocked  out  and 
then  the  2  by  4-inch  pieces  and  finally  the  boards. 

Another  type  of  small  culvert  and  form  as  used  by  the  Iowa  State  High- 
way Commission  is  shown  in  Fig.  33. 

75 


76 


77 


CIRCULAR   OR  PIPE  CULVERTS. 

Circular  or  pipe  culverts  are  made  of  concrete  as  in  Fig.  34,  or  of  metal 
with  concrete  head  walls  as  in  Fig.  35.  The  concrete  culvert  shown  is  3  feet 
in  diameter  and  is  not  reinforced.  An  apron  with  a  baffle  wall  on  each  side  as 
well  as  on  the  outer  end  is  provided  to  prevent  the  water  from  running 
the  outside  of  the  culvert  and  thus  washing  out  the  earth. 


P/an 


FIG.  34.— CONCRETE  CIRCULAR  CULVERT. 


Pipe  culverts  are  made  of  cast  iron  or  sheet  iron  or  of  tiles.  They  should 
have  fall  enough  so  that  water  will  not  stand  in  them,  a  slope  of  %  inch  per 
foot  being  generally  sufficient.  They  should  also  have  at  least  12  to  18  inches 
of  earth  over  the  top  of  the  pipe  and  the  earth  should  be  thoroughly?  com- 
pacted around  the  outside  of  the  pipe. 

To  prevent  undermining,  head  walls  should  always  be  used  with  pipe  cul- 
verts. In  Fig.  35  head  walls  for  four  sizes  of  metal  pipes  are  shown  and  they 
are  all  similar  except  that  for  the  24-inch  pipe  the  head  wall  has  a  coping 
6  inches  deep  projecting  2  inches  from  the  face  of  the  wall,  and  the  head  wall 
for  the  3-foot  pipe  has  a  concrete  apron  6  by  24  by  48  inches  in  size.  This 
apron  should  slope  up  at  the  inlet  and  down  at  the  outlet. 

78 


The  number  of  cubic  yards  of  concrete  in  one  head  wall  for  the  12.  18,  24, 
and  36-inch  pipe  is  0.64,  1.04,  1.47,  2.57  respectively.  The  2.57  cubic  yards  in 
the  headwall  for  the  36-inch  pipe  includes  the  concrete  in  one  apron. 

If  the  proportions  are  one  part  "ATLAS"  Portland  Cement,  two  and  one- 
half  parts  sand  and  five  parts  broken  stone  or  screened  gravel,  i  1/3  bbls.  ce- 
ment (each  barrel  being  the  same  as  four  bags)  will  be  required  for  a  cubic 
yard  together  with  about  y2  cubic  yard  of  sand  and  a  cubic  yard  of  broken 
stone  or  screened  gravel. 


-  6«O  > 

<^) 

>^rrr=>t 

E/ewf/on  ™£*<Secfian 

HEAD  WALL  rop  /&P/PE 

gag- 


M 

Secf/on  of  Apron 


11     ^ 

u  Vs-  Ivies-- • 

E/ewf/on  /npyane  of  face  of  Wff// 


HEAD  WALL  HDP 

FIG.  35.— CONCRETE  HEAD  WALLS  FOR  METAL  CULVERTS. 

ARCH  CULVERTS. 

As  previously  stated,  arch  culverts  are  more  expensive  and  more  difficult 
to  build  than  box  culverts,  but  nevertheless  they  are  frequently  used  where 
an  artistic  design  is  desirable.  The  culvert  of  5-foot  span,  illustrated  in  Fig. 
36,  is  very  similar  to  the  design  for  the  5-foot  span  shown  in  Fig.  39,  and  was 
built  in  Bureau  County,  Illinois,  by  the  Illinois  Gravel  Company  of  Princeton, 
Illinois.  It  contains  11.4  cubic  yards  of  concrete  mixed  one  part  "ATLAS" 
Portland  Cement  to  six  parts  sand  and  gravel,  using  gravel  as  the  large 
aggregate  with  coarse  sand  to  fill  the  voids.  The  cost  of  the  cement  delivered 


79 


at  the  bridge  was  $1.35  per  barrel.    Actual  cost  of  the  culvert  was  $75.00,  which 
included  long  haul  charges  for  gravel. 

Figs.  37,  38  and  39  show  designs  for  arch  culverts  of  5,  8,  and  lo-foot  clear 
spans  respectively,  suitable  for  highway  construction  where  the  soil  is  firm, 
as  compact  sand  or  hard  clay.  If  the  soil  is  soft  clay  or  loam,  the  footings 
should  be  made  wider  so  as  to  give  a  larger  bearing  area  for  the  walls  as  well 


FIG.  36.— CONCRETE  ARCH  CULVERT  IN  BUREAU  COUNTY,  ILLINOIS. 


as  for  the  arch  proper.  Of  course,  if  the  soil  is  too  soft,  box  instead  of  arch 
culverts  should  preferably  be  used,  or  else  the  bearing  power  of  the  soil 
should  be  increased  as  indicated  below  under  "Preparing  the  Bed." 

As  shown  in  Fig.  38,  each  end  wall  of  the  lo-foot  span  should  be  reinforced 
with  14  long  vertical  rods  and  with  8  short  bent  rods,  the  latter  extending 
horizontally  two  feet  into  the  arch  and  vertically  two  feet  into  the  end  walls ; 
and  in  addition  there  should  be  4  long  horizontal  rods  in  each  end  wall.  All 
rods  are  y*  inch  in  diameter.  The  5-foot  span  has  no  reinforcement  except 
5  bent  rods  to  tie  each  end  wall  to  the  arch. 

The  designs  show  a  width  of  10  feet  between  the  walls,  but  this  can  be 
increased  to  any  distance  desired. 

So 


LJ 


wevaf/on  of/Jrch 
w/fh  earfh  fitt/ng  removed 


'//*& 

Longifudina/  Section 

G ..J 


n  of  /J 
w/fh  earth  f/7//ng  removed 


FIG.  37.— ARCH  CULVERT  FOR  FIVE-FOOT  SPAN. 


ffei/af/on  of  4 re h 
w/tf)  e&tfh  fitting  removed 
H 


Note? 


-_.__  ._ 

-  1- 

t 

— 

± 

-1-    - 

-  .  

1 

"  t  " 

• 

1 

1 

1 

1 

1 

% 

| 

| 

1 

Sj 

i_t  i_l_'  J 

*   1 

I 

^ 

-3 

1— 

-I 

•  |-s- 

~    •—^-•-^- 

FYcn  ofdrch  wtf/7  earth  fitting  removed 


FIG.  38.— ARCH  CULVERT  FOR  TEN-FOOT  SPAN. 
8l 


ARCH  IN  BUREAU  CO.,  ILLINOIS 


BEAM  BRIDGE,  GROTON,  MASS. 
82 


In  the  5-foot  span  there  are  4.25  cubic  yards  in  each  end  wall  and  4.73 
cubic  yards  in  the  arch  between  the  end  walls,  making  a  total  of  13.23  cubic 
yards  of  concrete  in  the  structure.  In  case  the  roadway  is  wider  than  here 
assumed,  the  total  number  of  cubic  yards  of  concrete  in  the  structure  may  be 
computed  by  adding  to  8.5  the  product  of  0.473  times  the  distance  in  feet  be- 
tween the  end  walls;  8.5  being  the  cubic  yards  of  concrete  in  the  two  walls 
and  0.473  the  number  of  cubic  yards  of  concrete  in  one  foot  length  of  arch. 


M> 

i 


i 

i 

sy 

r 

£ 

fib 

'End  Elevation  ^ 

art.      AIIBodsi/n. 


Earth  filling 

i 


ngitudina!  Secf/on 


Plan 

FIG.  39.— ARCH  CULVERT  FOR  EIGHT-FOOT  SPAN. 


Thus,  if  the  roadway  were  16  feet  wide  instead  of  10  feet  the  total  volume 
of  concrete  in  the  culvert  is  8.5  plus  0.473  multiplied  by  16;  that  is,  8.5  plus  7.57 
or  16.07  cubic  yards. 

The  quantities  of  materials  for  arch  culverts,  5,  8  and  lo-foot  span,  are  given 
in  the  following  table. 


QUANTITY  OF  MATERIAL  FOR  ARCH  CULVERTS 
Proportions:  1  Part  "ATLAS"  Portland  Cement  to  2  1-2  Parts  Sand  to  5  Parts  Gravel  or  Stone 


Materials  for  Culvert  for  10-ft.  Roadway 
(See  Figs.  37,  38  and  39) 


Extra  Material  for  Each  Additional 
Foot  Width  of  Road 


Span 

Screened 

Screened 

of 

Cement 

Sand 

Gravel 

Cement 

Sand 

Gravel 

Culvert 

or  Stone 

or  Stone 

feet 

cu.  ft. 

cu  ft. 

cu.  ft. 

cu.  ft 

5 
8 

50  bags  or  12  y>  bbls. 
80    "     "  20    ~       " 

120 
190 

240 
380 

2  bags  or  ^  bbl. 
3    "    "     %    " 

5 

7^ 

10 

15 

10 

115    "     "  28  M 

275 

550 

4    «     ..      !    « 

10 

20 

PREPARING  THE  BED. 

Culverts  should  be  built  when  the  water  is  low  in  the  brook  at  the  site  of 
the  culvert.  In  many  cases  the  water  will  cause  no  trouble  if  in  excavating 
for  the  foundation  the  earth  is  thrown  up  into  two  parallel  dams  so  that  the 
brook  can  flow  between  them,  the  foundation  for  the  culvert  being  then  laid 
outside  of  these  piles  of  earth.  Sometimes  the  stream  can  be  carried  in  a  new 
trench  around  the  side.  If  there  is  considerable  water  in  the  brook  and  it 
cannot  be  carried  around,  it  may  be  necessary  before  excavating  to  drive  a 
row  of  closely  fitting  boards  parallel  to  the  stream  in  front  of  each  of  the 
proposed  trenches  in  which  the  foundations  are  to  be  laid  and  then  bank  the 
earth  against  the  boards  to  make  two  tight  dams  between  which  the  brook 
flows  and  behind  which  the  work  may  be  carried  on.  Sometimes  the  water 
may  be  carried  in  a  box  trough  as  shown  in  Fig.  41. 

In  some  cases  a  hand  pump  may  be  needed  to  keep  down  the  water  in 
trenches.  Trenches  for  foundations  of  whatever  kind  should  in  all  cases  be 
excavated  to  a  depth  below  frost,  but  if  the  brook  is  never  dry  two  or  three 
feet  below  the  bed  of  the  stream  will  be  sufficient. 

The  preparation  of  the  bottom  of  the  trenches  to  receive  the  concrete  foot- 
ings of  the  culvert  as  a  rule  should  not  be  difficult,  for  the  concrete  can  be 
laid  directly  on  the  soil  when  it  is  hard  clay,  compact  sand  or  gravel.  If  the 
soil  is  soft  sand  or  soft  clay  or  loam  it  should  be  compacted  by  ramming,  but 
if  too  soft  to  be  rammed  the  bearing  powetf  of  the  soil  can  be  increased  by 
adding  a  layer  of  clean  sand,  cinders,  or  broken  stone  before  ramming.  In 
extreme  cases,  where  the  soil  is  very  soft,  it  may  be  necessary  to  increase  the 
width  of  the  base  of  the  culvert  walls  or  to  build  these  walls  on  a  layer  of 
4-inch  planks  to  distribute  the  weight  over  a  considerable  area  of  the  soil. 


Occasionally,  piles  may  be  necessary.    Where  the  soil  is  as  soft  as  here  indi- 
cated a  box  culvert  is  preferable  to  an  arch. 

Planking  should  never  be  used  under  a  foundation  unless  it  will  at  all 
times  be  covered  with  water. 


FORMS  FOR  ARCH  CULVERTS. 

The  forms  are  set  after  the  soil  has  been  prepared  to  receive  the  concrete. 
Outer  wing  wall  forms  are  generally  constructed  of  i-inch  boards  laid  hori- 
zontally and  braced  with  2  by  4-inch  or  2  by  6-inch  studs.  The  forms  on  the 
inner  side  of  the  wing  walls  are  laid  horizontally  and  cut  to  fit  approximately 
the  shape  of  the  arch.  The  outer  surface  of  the  arch  proper  needs  forms  from 
the  bottom  up  to  about  ^  to  %  of  the  way  to  the  top  and  should  be  made  of 
i  by  4-inch  or  i  by  6-inch  boards,  attached  at  their  ends  to  the  inside  wing 
wall  forms. 

Centering  for  circular  arch  culverts  is  shown  in  Figs.  40  and  41.  The  sills 
should  be  set  first  and  braced ;  then  the  circular  forms,  spaced  2  feet  apart  for 
i -inch  lagging,  3  to  4  feet  apart  for  2-inch  stuff,  should  be  set  upon  the  wedges 
resting  on  the  upper  sills.  The  lagging  shown  in  the  drawings,  which  should 
be  of  narrow  width  to  fit  the  circle,  is  then  fastened  to  the  circular  centers. 
The  outer  forms  must  be  braced  by  tieing  across  the  top  of  the  culvert  or  by 
using  braces  against  the  earth  on  either  side. 

In  Fig.  41  the  inside  wall  forms  have  a  3  by  4-inch  or  a  4  by  4-inch  ranger 
set  across  the  top  of  the  cleats  on  which  the  wedges  are  placed  to  support  the 
arch  forms.  The  wedges  should  separate  the  two  forms  at  least  3  inches  in 
order  to  facilitate  the  removing  of  the  arch  forms.  A  strip  of  sheet  iron  may 
be  nailed  to  the  side  forms,  as  shown,  and  lap  over  on  to  the  arch  form  to 
prevent  the  concrete  from  getting  in  between  the  forms.  After  removing  the 
arch  forms  the  side  forms  can  be  readily  removed. 

The  forms  should  be  oiled  before  placing  the  concrete. 

The  concrete  for  culverts  should  be  of  a  mushy  consistency  and  should  be 
deposited  and  lightly  tamped  in  layers  6  or  8  inches  thick.  If  possible  the 
concrete  of  the  whole  arch  and  wing  walls  should  be  deposited  at  one  time, 
but  where  the  work  is  so  large  as  to  make  it  impossible  to  do  this,  the  arch 
should  be  divided  into  circular  sections,  and  one  section  laid  at  a  time. 
Twenty-eight  days  should  be  allowed  for  the  concrete  to  set,  after  which  time 
the  wedges  are  knocked  out  and  the  centers  removed.  The  earth  filling  can 
be  placed  as  soon  as  the  connecting  is  completed. 


FIG.  40.— FORMS  FOR  FIVE-FOOT  CIRCULAR  ARCH. 


^mjix4/n  Lagging 


41.— FORMS  FOR  EIGHT-FOOT  CIRCULAR  ARCS, 


CHAPTER  VI. 

BEAM  BRIDGES 

Owing  to  the  demand  for  more  permanent  bridges,  concrete  is  fast  replac- 
ing wood  and  steel  for  structures  of  all  types,  especially  for  spans  under  100 
feet.  Not  only  is  concrete  an  excellent  material  for  these  short  spans,  butl 
where  the  foundations  are  good,  concrete  arches  are  well  suited  even  for 
structures  200  feet  in  length  or  even  longer.  The  average  life  of  a  wooden 
bridge  is  only  about  9  years,  and  of  a  steel  bridge  not  over  30  to  40  years,  and 


FIG.  42.— CONCRETE  BEAM  BRIDGE. 

even  during  this  time  there  is  a  continual  outlay  for  repairs  and  painting.  A 
concrete  bridge  will  last  indefinitely  and  with  practically  no  maintenance. 

In  the  State  of  Illinois  alone  $1,888,724  was  expended  for  highway  bridges 
in  the  year  1905,  a  considerable  part  of  this  being  devoted  to  repairing  and 
replacing  wooden  or  metal  structures.  It  is  evident  that  more  attention  should 
be  given  to  the  design  and  construction  of  highway  bridges. 

In  addition  to  their  natural  permanence,  concrete  bridges  are  cheap  in  first 
cost  and  are  absolutely  proof  against  tornadoes,  high  water,  and  fire.  Further - 

87 


more,  by  employing  local  labor  the  money  spent  in  their  construction  remains 
almost  entirely  in  the  community  in  which  the  bridge  is  built,  there  is  less 
difficulty  in  securing  the  necessary  skilled  labor  during  times  when  the  build- 
ing trades  are  active  and  there  is  no  waiting  for  structural  steel  since  rods 
can  be  had  at  short  notice. 

The  greatest  care  should  be  taken  in  the  design  and  construction  of  con- 
crete bridges.  Designs  must  be  made  by  an  engineer  familiar  with  concrete 
construction  except  for  small  arched  structures  where  the  designs  given  in 
this  book  may  be  used  by  one  who  thoroughly  understands  the  use  of  concrete. 


KINDS  OF  CONCRETE  BRIDGES. 

Concrete  bridges  may  be  classified  as  flat  bridges  and  arch  bridges.  Flat 
bridges  are  those  in  which  the  pressure  from  the  bridge  acts  vertically  on  the 
supports  and  consist  either  of  straight  flat  slabs  or  of  combined  beams  and 
slabs  of  concrete  reinforced  with  steel.  Arch  bridges  are  curved  and  the 
pressures  upon  the  supports  are  not  vertical  but  inclined. 

Flat  construction  is  suitable  in  level  countries  for  short  spans,  generally 
not  exceeding  30  or  40  feet,  and  for  locations  where  the  foundation  is  soft 
material.  Arches  are  especially  economical  in  localities  where  the  roads  can 
be  built  considerably  above  the  streams  and  where  there  is  rock,  firm  sand 
or  gravel  or  other  similar  hard  soils  which  afford  good  foundations. 


TYPES  OF  FLAT  BRIDGES. 

Flat  bridges  may  be  divided  into  three  types,  slab,  combined  beam  and 
slab,  and  girder  bridges.  The  first  two  types  are  used  for  short  spans  and 
the  girder  type  is  preferably  used  for  spans  from  25  to  40  feet. 

A  slab  bridge,  Fig.  43,  consists  essentially  of  a  flat  slab  of  concrete  of 
uniform  thickness  reinforced  with  steel  and  resting  on  the  supporting  walls. 
In  some  cases,  as  shown  in  Fig.  44,  the  slab  is  supported  by  two  longitudinal 
girders.  The  macadam  roadway  is  laid  directly  on  the  slab — or  by  employing 
method  and  materials  described  in  Chapter  III  the  slab  may  form  a  concrete 
pavement. 

Combined  beam  and  slab  bridges,  Fig.  45,  consist  of  a  series  of  reinforced 
concrete  beams,  laid  parallel  to  the  roadway,  and  a  flat  slab  of  concrete  upon 
which  the  roadway  is  laid.  These  beams  rest  on,  and  are  usually  thoroughly 
united  with,  the  abutment  walls.  The  beams  and  slab  must  be  laid  at  one  time 
so  as  to  form  a  homogeneous  structure. 

88 


Girder  bridges,  Fig.  48,  are  usually  composed  of  two  large  reinforced  con- 
crete beams,  called  girders,  one  on  either  side  of  the  roadway  supporting  in- 
termediate cross  beams  which  in  turn  carry  the  slab  upon  which  the  roadway 
is  laid.  A  weight  on  the  roadway,  as  from  a  wagon  wheel  for  example,  is 
therefore  transmitted  from  the  roadway  to  the  slab,  then  to  the  beams,  then 
to  the  girders  and  finally  from  the  girders  to  the  supports. 

PROPORTIONS  FOR  CONCRETE. 

For  bridges  such  as  described  in  this  chapter,  the  concrete  should  he  mixed 
one  part  "ATLAS"  Portland  Cement,  two  parts  sand,  and  four  parts  broken 
stone  or  gravel  for  slabs,  beams,  girders,  and  other  parts  of  the  deck.  For 
abutment  walls  and  foundations  use  one  part  "ATLAS"  Portland  Cement, 
two  and  one-half  parts  sand,  and  five  parts  broken  stone  or  gravel. 

The  materials  must  be  thoroughly  mixed  and  must  not  be  separated  in 
handling. 

Care  must  be  taken  to  work  the  concrete  in  between  and  around  the  steel 
rods  without  displacing  them. 

The  forms  must  be  strong  and  under  the  bridge  they  must  be  left  in  place 
28  or  30  days  or  even  longer  in  the  fall  and  spring. 


STEEL  REINFORCEMENT. 

The  reinforcement  shown  in  the  designs  of  this  chapter  is  medium  steel, 
either  with  round  or  deformed  surfaces,  the  latter  giving  better  bond  with 
the  concrete. 

SLAB  BRIDGES. 

A  slab  bridge  similar  to  that  shown  in  Fig.  43,  representing  a  design  practi- 
cally the  same  as  the  standard  design  of  the  Pennsylvania  State  Highway 
Department,  is  of  simple  construction  and  permanent  character.  This  bridge, 
which  has  a  clear  span  of  16  feet,  consists  of  a  reinforced  slab  15  inches  thick 
connected  rigidly  to  two  abutment  walls  of  the  same  thickness.  The  side  walls 
serve  only  as  protecting  parapets.  The  principal  reinforcement  in  the  slab 
consists  of  steel  rods  ^4  mcn  square,  spaced  5  inches  apart  on  centers,  running 
lengthwise  of  the  roadway  and  bent  at  the  abutments.  The  design  shown 
differs  from  the  standard  of  the  Pennsylvania  State  Highway  Department  in 
that  alternate  bars  are  bent  upward  at  the  junction  of  the  slab  and  abutment 
walls  so  as  to  lie  near  the  outer  surfaces  of  the  slab  and  wall.  Rods  placed  in 
these  positions  at  the  upper  corners  prevent  cracks  from  forming  in  the  con- 
crete at  the  top  of  the  slab  near  the  abutment  wall.  In  addition  ^-inch  square 

89 


rods  are  used  in  the  slab,  abutments,  and  side  walls  as  shown  in  the  cut.  The 
distance  from  the  bottom  of  slab  to  top  of  upper  footing  course  is  shown  as 
6  feet,  but  this  may  be  increased  to  10  feet  if  necessary  to  give  the  proper 
waterway.  For  greater  heights  than  10  feet,  the  thickness  and  reinforcement 
of  the  walls  and  footings  should  be  increased.  The  total  length  of  each  side 
wall  also  must  be  increased  3  feet  for  every  i  foot  increase  in  the  height  over 
that  shown  in  the  cut. 


C.L  of  fibadway 


s 


*•£ 


/-/ALF  PLAN 





ELEVAT/ON  \  HAtr  LONG/TUD/NAL 

FIG.  43.— SLAB  BRIDGE  WITH  SPAN  OF  16  FEET, 


The  designs  for  spans  other  than  1 6-foot,  differ  in  the  thickness  of  the 
concrete  and  in  the  amount  of  reinforcement.  Each  span  is  a  special  design 
in  itself  and  it  is  just  as  necessary  to  have  exactly  the  correct  amount  of  con- 
crete and  steel  rods  for  each  individual  design  as  it  is  to  use  the  right  size  of 
I-beams  or  trusses  in  a  steel  bridge. 


90 


The  clear  width  of  the  roadway  in  the  design  illustrated  is  20  feet,  but 
this  may  be  changed  to  suit  local  conditions,  using  for  a  1 6-foot  span  the 
same  thickness  of  slab  and  the  same  size  and  spacing  of  reinforcement. 
There  are  73  cubic  yards  of  concrete  and  4,375  pounds  of  steel  rods  in  this 
bridge.  For  every  i-foot  increase  or  decrease  in  width  of  roadway,  there  will 
be  an  increase  or  decrease  in  the  volume  of  concrete  of  1.91  cubic  yards,  and 
in  the  weight  of  steel  rods  of  125.7  pounds.  With  the  aid  of  these  figureSj 
the  total  quantities  may  be  computed  for  a  bridge  having  a  roadway  whose 
width  differs  from  that  shown  in  the  drawing. 

The  accompanying  table  shows  the  proper  dimensions  and  quantities  of 
materials  for  slab  bridges  similar  to  that  illustrated  in  Fig.  43.  The  quan- 
tities of  materials  given  in  the  table  are  for  the  entire  bridge,  including  abut- 
ments, sidewalls  and  slab. 

PRINCIPAL  DIMENSIONS   AND   QUANTITIES   OF   MATERIALS  FOR  SLAB   BRIDGES 

SIMILAR  TO  BRIDGE  IN  FIG.  43 


Clear 

Thick- 
ness of 

Longitudinal 
Bars 

Abutment 
Walls 

Length  of 
Side  Walls, 
Feet 

Cu.  Yds.  of 
Concrete 

Pounds  of 
Steel  Rods 

Span 

Slab 

in  Ft 

in 
Inches 

Size  of 
Square 
Bars, 
Inches 

Distance 
c.  to  c., 
Inches 

Thick- 
ness, 
Inches 

Width  of 
Footing, 
Inches 

6  Ft.* 

8  Ft.* 

6  Ft.* 

8  Ft.* 

6  Ft.* 

8  Ft.* 

8 

9 

H 

6 

8 

20 

32.0 

38.0 

43 

53 

2715 

3440 

10 

11 

H 

5 

11 

23 

34.5 

40.5 

49 

60 

3195 

3880 

12 

13 

% 

5 

13 

27 

37.0 

43.0 

57 

69 

3420     4100 

16 

15 

U 

5 

15 

45 

41.5 

47.5 

73 

87 

4375 

5035 

*Distance  in  feet  from  top  of  footing  course  to  bottom  of  slab. 


A  slightly  different  style  of  design  for  a  slab  bridge  from  that  just  de- 
scribed is  shown  in  Fig.  44,  which  represents  a  standard  design  of  the  Illinois 
State  Highway  Commission  for  a  24-foot  span  carrying  a  roadway  16  feet 
wide.  Here  the  slab  is  supported  by  the  side  girders  which  at  the  same  time 
serve  as  side  railings  or  parapets.  The  wing  walls  are  set  at  an  angle  with 
the  abutments  and  are  reinforced  with  ^2-inch  rods  laid  horizontally  near 
the  front  face  and  vertically  near  the  back  face.  The  main  abutment  walls 
are  14  inches  thick  and  have  a  maximum  height  of  14  feet  4  inches  from  the 
bottom  of  the  foundation.  These  walls  as  well  as  their  foundations  are 
reinforced  with  ^-inch  bars  as  indicated  in  the  figure. 

The  floor  slab  is  n  inches  thick  and  is  reinforced  with  ^4-inch  bars,  4 
inches  apart  on  centers  running  across  the  roadway  ancj  bent  up  into  the  gir- 


N.II,!.!.!^:,;.;!     ;_ 

lp^%ffll" 


FIG.  44.— SLAB  BRIDGE  WITH  SPAN  OF  24  FEET.    , 


ders,  also  with  %-'mch  bars  spaced  12  inches  apart  on  centers  running  length- 
wise of  the  bridge.  The  reinforcement  of  the  girders  consists  of  nine  hori- 
zontal bars  imbedded  in  the  lower  part  and  several  U-shaped  bars  placed  ver- 
tically at  short  intervals  throughout  the  length  of  the  beam. 

Care  must  be  taken  to  set  the  steel  rods  in  the  places  called  for  by  the 
plans;  thus,  in  the  footings  of  the  abutment  walls  the  horizontal  rods  must 
be  near  the  bottom,  not  the  top  of  each  footing.  Rods  are  placed  in  concrete 
to  perform  certain  definite  purposes  and  too  much  care  cannot  be  taken  to 
see  that  they  are  set  right  and  that  they  do  not  get  moved  out  of  place  during 
the  progress  of  the  work. 

In  this  24-foot  span,  shown  in  Fig.  44,  there  are  82.7  cubic  yards  of  concrete 
and  7,584  pounds  of  steel. 


COMBINED   BEAM  AND   SLAB  BRIDGES. 

Combined  beam  and  slab  bridges  are  more  complicated  in  design  and  in 
construction  than  are  slab  bridges.  Inexperienced  persons  should  not  at- 
tempt the  design  of  structures  of  this  type  and  those  ignorant  of  the  use  of 
concrete  should  not  attempt  to  build  beam  and  slab  bridges. 

Combined  beam  and  slab  bridges  are  well  adapted  to  spans  of  15  to  30 
feet  where  the  width  of  roadway  is  more  than  16  or  18  feet.  Fi&  45  shows 
such  a  structure  built  of  reinforced  concrete  in  1906  by  the  Massachusetts 
Highway  Commission  and  represents  a  skew  bridge  of  28-foot  span.  The 
slab  on  which  the  macadam  roadway  is  laid  is  4  inches  in  thickness  and  is 
reinforced  with  %-inch  square  twisted  steel  rods  spaced  8  inches  apart.  The 
slab  is  supported  by  eight  reinforced  concrete  beams  spaced  3  feet  2  inches 
apart  on  centers.  These  beams  are  28  inches  deep  under  the  slab  and  vary 
in  width  from  13  inches  on  the  bottom  to  14  inches  just  under  the  slab.  The 
reinforcement  for  each  beam  consists  of  three  longitudinal  i%-inch  square 
twisted  rods  placed  near  the  bottom  with  ten  ^g-inch  and  six  J^-inch  stirrups 
placed  as  shown  in  the  longitudinal  section  of  beam. 

In  the  construction  of  concrete  beams,  such  as  that  shown  in  Fig.  45, 
running  parallel  with  the  roadway  and  resting  upon  the  abutment  cross  walls, 
the  best  design  demands  that  one  or  more  bent  bars  be  placed  in  each  end 
of  each  beam  running  vertically  into  the  wall  near  the  back  face  and  horizon- 
tally into  the  beam  near  the  top  surface  of  the  beam.  Bent  rods  of  this  kind 
tend  to  prevent  the  formation  of  cracks  in  the  upper  surface  of  the  beam  near 
the  ends.  In  the  longitudinal  beams  in  Fig.  45,  this  can  be  done  by  bending 
up  the  center  1%-inch  bar  about  3  feet  from  the  face  of  each  abutment  and 

93 


94 


continuing  this  bar  near  the  upper  horizontal  surface  of  the  beam  thence 
around  the  corner  down  into  the  abutment  walls  about  4  feet. 

The  abutments,  Fig.  45,  which  are  irregular  in  shape  on  account  of  the 
skew  on  which  the  bridge  crosses  the  stream,  are  braced  with  counterforts 
15  inches  thick  spaced  about  5  feet  apart.  Each  counterfort  has  two  ^g-inch 
tie  bars  imbedded  2*4  inches  in  from  the  back  surface  and  bent  down  into  the 
footing  so  as  to  form  a  secure  tie.  The  footing  is  also  reinforced  with  %-inch 
bars  running  perpendicular  to  the  face  of  the  abutment  and  spaced  12  inches 
apart  on  centers.  The  abutment  and  wing  walls  are  15  inches  thick  and 
have  ^/2-inch  horizontal  bars  spaced  from  12  to  24  inches  apart  on  centers  and 
s/g-inch  vertical  bars  6  inches  apart  on  centers. 


FIG.  46.— FORMS  FOR  SLAB  AND  BEAM  BRIDGE. 

One  hundred  and  seventy-seven  cubic  yards  of  1 12  15  "ATLAS"  Portland 
Cement  concrete  were  used  in  the  construction  of  this  bridge.  The  total  cost 
of  the  bridge  was  $2,286.50,  the  cement  costing  $2.30  at  the  nearest  railroad 
station.  The  actual  time  of  construction  was  54  days,  although  the  total  time 
elapsing  from  start  to  finish  of  the  work  was  86  days. 

In  concreting  a  combined  beam  and  slab  bridge,  the  work  must  be  con- 
tinuous so  that  the  beam  and  slab  are  placed  at  one  time,  thus  forming  a 
monolith.  This  is  a  very  important  matter  and  utmost  precautions  must  be 
taken  to  see  that  it  is  carried  out  in  the  construction  of  beam  and  slab  bridges. 

95 


FIG.  47.— FORMS  FOR  DECK  OF  COMBINED  BEAM  AND  SLAB  BRIDGE. 

96 


METHOD  OF  CONSTRUCTION  OF  COMBINED  BEAM  AND  SLAB 

,       BRIDGES. 

Fig.  47  shows  the  arrangement  of  forms  for  the  deck  of  a  combined  beam 
and  slab  bridge.  Generally  the  abutment  forms  are  first  set  and  the  concrete 
placed  to  the  grade  of  the  bottom  of  the  beams  in  the  deck.  The  forms  for 
the  deck  are  then  put  into  position  and  after  the  reinforcement  is  placed  the 
concrete  for  the  beams  and  slab  is  laid,  the  concrete  for  the  slab  being  placed 
immediately  after  filling  the  beam  form  below  it  and  before  the  cement  begins 
to  set.  In  some  cases  where  the  beams  underneath  the  slab  are  designed 
heavy  enough  to  act  alone  without  the  aid  of  the  slab  the  beam  reinforcement 
is  first  placed  and  the  concrete  for  the  beams  poured  into  the  forms.  Then 
the  slab  reinforcement  is  placed  in  position  and  the  concreting  of  the  slab 
started.  If,  however,  the  beams  are  designed  as  T-beams  in  the  more  usual 
and  the  cheapest  way,  it  is  absolutely  essential  that  the  beams  and  slab  be 
laid  at  the  same  operation.  The  deck  forms  should  be  thoroughly  braced 
underneath  so  that  they  will  not  deflect  as  the  concrete  is  poured. 

In  Fig.  47  the  bracing  is  only  partially  shown,  since  it  will  vary  consider- 
ably with  the  location  of  the  structure.  The  stirrups  shown  in  section  A-A 
can  best  be  held  in  place  temporarily  with  small  wooden  strips  which  are 
removed  as  soon  as  there  is  enough  concrete  in  the  beam  to  hold  the  stirrups 
in  place. 

GIRDER  BRIDGES. 

Concrete  girder  bridges  are  not  so  common  as  slab  or  combined  slab  and 
beam  bridges,  but  they  are  suitable  for  spans  longer  than  is  proper  for  the 
slab  bridges  and  for  locations  where  there  is  not  head  room  enough  to  use  an 
arch  span.  Fig.  44  is  in  one  sense  a  girder  bridge  since  it  has  two  main 
girders  which  carry  the  slab,  but  Fig.  48  gives  a  better  idea  of  this  type  of 
structure.  In  Fig.  48  the  slab  is  8  inches  in  thickness  at  the  center  and  7 
inches  at  the  girders  and  is  reinforced  with  ^-inch  twisted  square  bars  spaced 
7  inches  apart  on  centers  running  parallel  to  the  roadway.  At  the  center  of 
each  panel,  that  is,  midway  between  the  cross  floor  beams,  these  bars  must 
be  laid  i%  inches  from  the  bottom  of  the  slab,  but  at  the  cross-beams  they 
should  be  i*/2  inches  from  the  top  of  the  slab,  being  bent  to  conform  to  these 
requirements.  Another  way  is  that  shown  in  Fig.  48,  where  the  rods  in  the 
bottom  of  the  slab  are  run  through  straight  over  the  floor  beams  and  another 
set  of  %-inch  bars  4  feet  long  spaced  7  inches  apart  on  centers  is  laid  parallel 
with  the  length  of  the  roadway  and  imbedded  in  the  top  of  the  slab  over  the 
floor  beam.  At  the  end  of  the  bridge  where  the  slab  connects  with  the  end 

97 


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98 


floor  beam,  the  rods  in  the  top  of  the  slabs  should  be  bent  to  extend  downward 
into  the  floor  beam. 

The  floor  beams,  which  are  the  cross-beams  running  from  girder  to  girder, 
are  spaced  10  feet  apart  on  centers  and  are  reinforced  with  five  %-inch  longi- 
tudinal bars  and  with  ^4-inch  stirrups.  These  longitudinal  rods  must  be  bent 
up  at  each  of  the  floor  beams  as  shown  and  must  extend  into  the  girder. 

The  main  girders  have  a  clear  span  of  37  feet  and  a  depth  of  5  feet.  They 
are  reinforced  with  eight  i*4-inch  square  bars  in  the  bottom  and  three  i%- 
inch  square  bars  in  the  top  and  are  provided  with  vertical  stirrups.  The  stir- 
rups are  */2-inch  bars  bent  U-shaped  and  placed  close  together  near  the  ends 
of  the  girder  and  further  apart  near  the  center. 

The  surface  of  the  roadway  must  be  drained  and  this  can  best  be  done  by 
making  a  slab  with  a  curved  upper  surface  so  that  the  water  may  run  to  the 
gutters  and  thence  through  the  drain  pipes  placed  in  the  slab. 


FIG.  49.— REINFORCED  CONCRETE  ROADWAY  FOR  STEEL  SPANS. 

CONCRETE  FLOORS  FOR  STEEL  BRIDGES. 

On  long  span  highway  bridges  where  steel  trusses  are  necessary,  plank 
flooring  has  until  recently  been  used,  but  as  this  planking  only  lasts  from  one 
to  five  years  there  is  a  demand  for  something  more  durable  than  wood  and 
reinforced  concrete  slabs  on  steel  beams  are  being  used. 

Fig.  49  shows  a  typical  cross  section  of  a  concrete  slab  construction  carried 
on  steel  I-beam  stringers  which  in  turn  are  supported  by  the  steel  floor  beams 
running  from  truss  to  truss.  A  so-foot  roadway  without  sidewalks  is  here 
provided  for,  but  where  sidewalks  are  necessary  the  construction  may  be  easily 
modified  to  suit.  The  wearing  surface  of  the  roadway  is  shown  as  asphalt, 
which  usually  is  laid  2  inches  thick  on  a  binder  of  small  thickness.  In  some 
cases  the  binder  has  been  omitted  and  the  upper  surface  of  the  concrete  left 

99 


very  rough  to  give  a  good  union  between  asphalt  and  concrete.  Proper  crown 
must  be  given  the  roadway  to  take  care  of  the  drainage ;  this  being  easily  done 
by  setting  the  I-beam  stringers  on  high  levels  towards  the  center  of  the  road- 
way or  else  by  making  the  concrete  slab  level  and  using  a  greater  thickness  of 
wearing  surface  at  the  center  than  at  the  gutters. 

The  I-bearri  stringers  should  be  encased  in  concrete  as  shown,  for  by  so 
doing  a  stronger  floor  is  obtained  and  the  steel  beams  are  protected  against 
rust.  Railing  posts  made  of  two  steel  angles  and  connected  to  the  outside  I- 
beam  by  a  plate  and  small  angles,  give  the  necessary  support  to  the  railings. 

COST  OF  BEAM  AND  SLAB  BRIDGES. 

There  is  considerable  variation  in  the  cost  of  concrete  bridges  and  any  data 
given  regarding  the  cost  is  at  the  best  only  approximate.  The  cost  of  a  bridge 
is  affected  by  the  span,  width,  height,  character  and  depth  of  foundations,  the 
type  of  structure,  the  magnitude  of  the  loads  to  be  carried,  the  style  of  finish, 
and  by  several  other  elements  of  a  similar  nature. 

The  cost  of  several  reinforced  concrete  bridges  recently  built  and  similar  to 
those  shown  in  this  chapter,  was  $9.00  per  cubic  yard  for  the  reinforced  con- 
crete where  the  expense  of  hauling  was  considerable,  and  $6.75  per  cubic  yard 
for  abutments  without  reinforcement.  The  abutment  foundations  extended 
about  3  feet  into  the  ground. 

For  reinforced  concrete  bridge  work  similar  to  that  shown  in  Fig.  43,  the 
contract  price  frequently  paid  by  the  Pennsylvania  State  Highway  Commis- 
sion is  $10.00  per  cubic  yard. 

A  bridge  of  30  feet  span  similar  to  the  one  shown  in  Fig.  44  and  designed 
by  the  Illinois  Highway  Commission  cost  $995  not  including  the  crushed  stone 
which  was  furnished  free.  The  price  of  the  bridge  would  have  been  $1,125  nacl 
the  contractor  furnished  everything.  There  were  90  cubic  yards  of  concrete 
and  8,600  Ibs.  of  steel  in  the  structure.* 


*Illinois  Highway  Commission  Report,  1906,  p.  59. 

100 


CHAPTER  VII. 

ARCH  BRIDGES. 

Arches  include  that  class  of  curved  bridges  varying  from  simple  culverts  of 
5  or  lo-foot  spans  to  the  wonderful  structures  like  the  Walnut  Lane  Bridge  in 
Philadelphia  which  has  an  arch  of  232  feet,  clear  span.  The  advantage  of 
using  concrete  in  bridges  was  clearly  set  forth  in  Chapter  VI.  and  therefore  it 
is  needless  to  further  emphasize  in  this  chapter  on  arch  bridges,  its  value 


AUBURN  ST.  BRIDGE,  MEDFORD,  MASS. 

wherever  ultimate  economy,  beauty  and  durability  are  of  importance.  Suffice 
it  to  say  that  in  many  locations  a  good  concrete  arch  bridge  can  be  built 
cheaper  than  a  good  steel  bridge,  and  when  the  durability  of  the  concrete  and 
the  enormous  cost  of  maintaining  the  steel  bridge  are  considered  there  is  no 
question  as  to  which  is  the  better  investment  for  a  town  or  county  to  make. 
The  concrete  structure  is  more  durable,  more  beautiful,  and  in  every  way  supe- 
rior to  steel  construction  for  spans  of  ordinary  length.  Where  the  foundations 
are  good,  a  series  of  arches  may  be  used  in  place  of  a  steel  bridge  with  long 
spans,  and  the  advantages  already  enumerated  for  short  spans  apply  equally 
well  in  this  case.  The  pressures  which  the  arch  exerts  on  its  foundations  are 


IOI 


inclined  'arid  this  pressure  or  outward  thrust  must  be  provided  for  in  the  design 
and  construction  of  the  bridge. 

PLAIN  AND  REINFORCED  CONCRETE  ARCHES. 

Arches  may  be  built  either  with  or  without  steel  reinforcing  bars;  where 
there  is  no  steel  the  arch  is  of  plain  concrete,  and  if  steel  rods  or  steel  in  other 
forms  are  used  to  reinforce  the  concrete  the  structure  is  then  called  a  reinforced 
concrete  arch  bridge. 

Steel  reinforcements  should  always  be  used  in  arches,  for  while  it  adds  very 


BRIDGE  IN  DELLWOOD  PARK,  JOLIET,  ILL.  - 

little  to  the  cost,  it  increases  the  strength  considerably.  In  the  last  few  years 
there  has  been  a  remarkable  increase  in  the  number  of  reinforced  concrete  arch 
bridges,  and  they  are  giving  perfect  satisfaction.  In  most  cases  the  quantity  of 
steel  used  is  really  very  small  in  proportion  to  the  quantity  of  concrete,  and  as 
this  steel  is  entirely  imbedded  in  the  concrete  it  cannot  rust  and  therefore  is  not 
open  to  the  same  objections  that  are  raised  against  steel  where  it  is  exposed  to 
the  action  of  the  elements.  In  many  arches  the  cross-sectional  area  of  the  steel 
used  is  only  about  i/ioo  of  the  area  of  the  concrete  as  measured  at  the  crown 
of  the  arch,  which  is  the  highest  part  of  the  span.  This  means  that  for  every 
100  square  inches  of  concrete  there  is  only  i  square  inch  of  steel  at  that 
section., 

1 02 


Under  ordinary  conditions  bridges  of  spans  from  20  or  30  feet  to  100  feet 
can  be  readily  constructed  of  reinforced  concrete,  while  for  even  greater  spans 
where  the  foundations  are  good,  the  proper  combination  of  steel  and  concrete 
makes  a  strong,  graceful  and  economical  bridge,  a  type  which  is  being  widely 
adopted  in  country  districts  as  well  as  in  the  larger  towns. 

HISTORY  OF  CONCRETE  ARCHES. 

The  first  plain  concrete  arch  built  was  the  n  6-foot  span  at  Fontainebleau 
Forest  in  France,  which  was  finished  in  1869,  and  is  known  as  the  Grand  Maitre 
bridge.  In  the  United  States  the  first  plain  concrete  arch  of  which  there  is  any 
record  was  one  of  3i-foot  span  built  in  1871  in  Prospect  Park,  Brooklyn.  The 
earliest  reinforced  concrete  arch  in  the  United  States  was  constructed  in 
Golden  Gate  Park  in  San  Francisco  in  1889,  and  several  years  even  before  this 
date  concrete  bridges  reinforced  with  iron  had  been  built  in  Europe.  This 
type  of  construction  is  not  an  experiment.  It  represents  the  highest  art  of 
modern  bridge  construction.  As  a  material  for  highway  bridges  of  spans  from 
about  30  feet  to  100  feet  reinforced  concrete  has  no  equal. 

As  has  already  been  stated,  a  span  of  232  feet  has  been  completed  in  Phila- 
delphia. The  new  Rocky  River  Bridge  in  Cleveland,  Ohio,  is  being  con- 
structed with  a  span  of  280  feet  and  a  proposed  bridge  in  New  York  City  has  a 
span  of  over  700  feet.  These  large  spans  show  the  rapid  development  in  the 
art  of  building  bridges  with  concrete. 

TYPES  OF  CONCRETE  ARCHES. 

Arches  are  classified  in  various  ways,  but  the  most  simple  classification  is 
that  which  deals  with  the  method  of  the  construction  of  the  spandrels  which 
are  the  spaces  above  the  upper  surface  of  the  arch  ring  and  below  the  roadway 
level.  These  spaces  may  be  either  filled  in  solid  with  earth  filling  or  they  may 
be  left  open  by  supporting  the  roadway  above  on  slabs  and  beams,  which  in 
turn  are  supported  on  columns  or  cross-walls  resting  on  the  arch  ring. 

Where  the  spandrel  spaces  are  filled  in  solid  with  earth,  this  earth  is  pre- 
vented from  flowing  out  sidewise  by  side  walls,  also  called  spandrel  walls, 
which  run  lengthwise  of  the  bridge,  one  on  either  side  of  the  roadway.  The 
earth  rests  directly  on  the  outer  surface  of  the  arch  ring  and  the  road  or  street 
pavement  is  laid  directly  on  this  earth  filling.  These  bridges  are  said  to  have 
solid  spandrels. 

In  the  second  type,  where  the  spandrels  are  left  more  or  less  open,  the  road- 
way is  usually  laid  on  a  slab  of  reinforced  concrete  having  a  thickness  of  from 
4  to  8  inches  which  rests  upon  a  series  of  reinforced  beams  supported  on  col- 

103 


umns,  or  upon  transverse  concrete  walls  which,  being  spaced  at  distances  of 
from  10  to  20  feet  lengthwise  of  the  bridge,  give  the  appearance  of  open  span- 
drels. These  columns  or  walls  rest  on  top  of  the  arch  ring. 

For  small  arches  the  solid  spandrel  type  is  the  most  common,  while  for  the 
large  bridges  with  spans  over  100  feet  the  open  spandrels  are  better,  because 
they  lessen  the  weight  to  be  carried. 

Arches  are  often  also  classified  as  to  the  style  of  reinforcement  or  as  to 
whether  there  are  any  hinges  used  in  the  arch  ring.  A  hinge  is  made  by  insert- 
ing a  joint  in  the  concrete  arch  ring,  and  usually,  when  they  are  used,  one  is 


FIG.  50.— ARCH  BRIDGE,  DELLWOOD  PARK,  JOLIET,  ILLINOIS. 

placed  at  the  crown  of  the  arch  and  also  one  at  each  end  where  the  arch  ring 
rests  upon  the  abutment  or  support.  These  hinges  are  made  of  steel  and  act 
very  much  in  principle  like  the  hinges  on  an  open  door,  that  is,  the  concrete 
arch  ring  can  move  a  little  by  turning  around  the  steel  hinges.  This  movement 
is  of  course  very  small.  Hinges  are  used  with  an  idea  of  simplifying  the 
design  of  the  arch,  but  they  have  been  employed  in  only  a  few  cases  in  the 
United  States. 


PREPARATION  OF  PLANS. 

An  arch  bridge  is  too  important  a  structure  to  be  placed  in  charge  of  an 
inexperienced  man.  The  only  safe  way  is  to  employ  a  competent  engineer  to 
prepare  plans  and  specifications  and  to  superintend  the  construction.  Before 

104 


the  contract  for  the  bridge  is  let,  the  plans  should  be  complete  and  should  show 
not  only  the  principal  dimensions  of  the  structure,  but  they  should  also  show 
all  important  details  which  may  in  any  way  affect  the  strength  or  the  cost. 
Unless  the  plans  and  specifications  are  complete  and  accurate,  unnecessary 
delays  in  construction  and  extra  charges  for  changes  and  additions  will  inev- 
itably occur.  If  the  engineer  is  not  to  be  on  the  ground  continually  during  the 
construction,  he  should  be  allowed  a  competent  assistant  or  inspector  whose 
duty  it  should  be  to  see  that  the  plans  and  specifications  are  followed  and  that 
the  work  is  carried  on  in  a  proper  manner. 

DESIGN  FOR  A  4o-FOOT  SPAN. 

Fig.  51  shows  a  design  for  a  reinforced  concrete  highway  arch  for  a  4O-foot 
span  with  a  rise  of  8  feet.  The  principal  parts  are  the  arch  ring,  the  spandrel 
or  side  walls,  the  abutments,  the  wing  walls,  the  parapets  and  the  earth  filling. 
The  cross  section  at  crown  shows  a  2o-foot  roadway  with  a  6-foot  sidewalk  on 
either  side.  At  the  crown  of  the  arch  the  earth  filling  has  a  thickness  of  18 
inches  at  the  center  of  the  roadway. 

The  arch  ring  is  12  inches  thick  at  the  crown  and  2  feet  6  inches  thick  at  the 
abutments,  the  latter  being  the  radial  not  the  vertical  thickness.  The  dimen- 
sions of  the  abutments  are  shown  in  the  drawing  and  have  been  determined  on 
the  assumption  that  the  soil  under  the  foundations  is  good  compact  sand  and 
gravel  or  other  similar  materials  capable  of  safely  sustaining  4000  to  6000  Ibs. 
per  square  foot. 

The  arch  ring  is  reinforced  with  round  medium  steel  rods  54  inch  m  diam- 
eter running  lengthwise  of  the  span,  arranged  in  two  layers,  one  layer  2  inches 
in  from  the  outer  curved  surface  of  the  concrete  ring  and  the  other  2  inches 
from  the  inner  curved  surface.  These  layers,  therefore,  are  8  inches  apart  at 
the  crown  and  2  feet  2  inches  apart  at  the  abutments.  The  rods  in  each  layer 
are  8  inches  apart  on  centers  as  shown  in  the  cross  section. 

In  addition  to  the  ^-inch  rods  there  are  two  sets  of  %-inch  diameter  rods 
running  at  right  angles  to  the  length  of  the  roadway  as  shown  in  the  one-half 
longitudinal  section.  In  each  layer  the  5/2 -inch  rods  are  15  inches  apart  on 
centers.  Stirrups  made  of  J^-inch  diameter  round  rods  are  frequently  used  in 
bridges  of  this  type  to  connect  the  outer  layer  with  the  inner.  They  should  be 
hooked  at  the  outer  and  inner  ends  to  pass  around  the  transverse  and  longi- 
tudinal rods  at  their  intersections.  In  the  bridge  shown,  this  arrangement 
would  space  them  15  inches  apart.  Where  no  stirrups  are  used,  the  transverse 
and  longitudinal  rods  should  be  connected  by  wires  at  their  intersections. 

Where  the  design  calls  for  rods  longer  than  can  be  obtained  in  one  length, 
splices  must  be  used  and  this  can  be  done  by  simply  lapping  the  two  bars  to 

105 


%    B 


106 


be  spliced  a  distance  equal  to  20  diameters  of  the  rod  if  it  has  deformed  sur- 
faces or  30  diameters  if  it  has  smooth  surfaces.  Sometimes  the  rods  are  lapped 
and  then  wound  with  heavy  wire.  Some  designers  thread  the  rods  and  splice 
them  by  means  of  sleeve  nuts,  but  usually  it  is  sufficient  to  lap  the  rods  as 
indicated. 

As  shown  in  the  cross  section  at  the  crown,  Fig.  51,  six  ^-inch  diameter 
rods  should  be  placed  in  the  parapet  wall  between  the  expansion  joints. 

The  design  shown  is  suitable  for  ordinary  highway  traffic. 

EXPANSION  JOINTS. 

Each  spandrel  wall  and  parapet  is  provided  with  an  expansion  joint  at  the 
abutments.  This  is  to  allow  for  the  change  in  length  of  these  parts  due  to 
changes  in  temperature.  Concrete  changes  its  length  about  ^4-inch  for  every 
100  feet  of  length  due  to  the  change  in  temperature  from  a  mean  temperature 
to  extreme  heat  or  to  extreme  cold  in  a  climate  such  as  that  of  New  England, 
Michigan  or  similar  sections.  Unless  the  wall  is  properly  reinforced,  expansion 
joints  should  be  left  at  distances  apart  not  much  over  40  feet  or  even  less  to 
prevent  cracking  due  to  these  changes  in  temperature.  These  joints  should  be 
made  from  the  upper  surface  of  the  arch  ring  to  the  top  of  the  parapet  and 
should  be  made  wedge-shaped  or  dove-tailed  so  that  one  part  fits  into  the  other. 

REINFORCED  CONCRETE  ARCH,  ELM  STREET,  CONCORD,  MASS. 

Figs.  52  and  53  show  a  highway  bridge  of  75  feet  clear  span  built  of 
"ATLAS  "Portland  Cement  in  Concord,  Massachusetts,  by  the  Massachusetts 
Highway  Commission.  The  rise  of  the  arch  is  12  feet  or  about  1/6  of  the  span 
length.  At  the  crown  the  arch  ring  is  16  inches  in  thickness  and  increases 
towards  the  abutments  as  shown. 

The  reinforcement  in  the  arch  ring  consists  of  i-inch  longitudinal  twisted 
steel  bars  spaced  17  inches  apart  on  centers  and  %-inch  transverse  twisted 
steel  bars  spaced  24  inches  apart  on  centers.  The  centers  of  the  i-inch  rods 
are  2%  inches  from  the  face  of  the  concrete  and  these  rods  are  in  lengths  of 
about  1 6  feet  lapped  40  inches  at  each  splice  as  shown  in  Fig.  55.  Reinforced 
side  walls  braced  with  counterforts  shown  in  Fig.  53  serve  to  retain  the  earth 
filling.  Although  there  is  a  comparatively  small  amount  of  concrete  used  in 
the  construction  of  this  type  of  wall,  the  saving  due  to  this  is  probably  more 
than  offset  by  the  increase  in  cost  due  to  the  expensive  forms  necessary  for 
the  counterforts.  Several  sections  of  these  side  walls  are  shown  in  the  upper 
right  hand  corner  of  the  drawing  over  the  half  section  of  the  arch,  and  the 
locations  of  these  sections  are  indicated  by  distances  on  the  half  section  and 

107 


by  letters  upon  the  plan  of  the  arch.  The  steel  in  the  side  walls  consists  of 
54-inch  horizontal  rods  spaced  12  inches  apart  on  centers  near  the  bottom  and 
5/2-inch  rods  spaced  24  inches  apart  on  centers  near  the  top  of  the  wall.  In  the 
coping  there  are  also  two  %-inch  longitudinal  rods.  The  counterforts  are  pro- 
vided with  tie  rods  as  indicated. 

As  shown  in  Fig.  53,  the  coping  overhangs  the  face  of  the  arch  ring  and  the 
face  of  the  wing  walls  by  154  inches,  the  faces  just  mentioned  being  in  the 
same  vertical  plane ;  the  spandrel  walls  are  set  back  i  */£  inches  from  the  face  of 
the  arch  ring,  hence  3  inches  back  from  the  surface  of  the  coping.  This  gives 
a  neat  design  and  one  which  is  easily  carried  out. 

Four  hundred  and  fifty-eight  cubic  yards  of  concrete  were  used  in  this 
structure. 


FIG.  52.— ARCH  BRIDGE  WITH  SPAN  OF  75  FEET,  ELM  STREET,  CONCORD,  MASS. 

( 

Fig.  54  on  page  no  is  a  view  taken  just  after  the  falsework  and  centering 
were  in  place  and  before  the  lagging  was  placed  on  the  centering.  The  pho- 
tograph on  page  no  shows  the  arch  ring  under  construction  with  the  longitudi- 
nal rods  partially  imbedded  in  concrete.  One  of  the  small  transverse  rods  may 
be  seen  just  beyond  the  top  of  the  transverse  stop  boards.  These  stop  boards 
serve  as  temporary  forms  for  the  concrete  and  also  as  spacers  for  the  longi- 
tudinal rods.  After  these  boards  are  removed  the  next  section  of  the  concrete 

108 


109 


FIG.  54.— CENTERING  OF  ARCH  BRIDGE,  ELM  STREET,  CONCORD,  MAii. 


FIG.  55.— CONSTRUCTION  OF  ARCH  BRIDGE,  ELM  STREET,  CONCORD,  MASS. 

110 


for  the  arch  ring  is  deposited  against  the  finished  section.  The  form  of  arch 
here  shown  is  suitable  for  locations  where  the  foundation  is  of  the  hardest 
material,  like  hard  pan  or  rock. 

FALSEWORK  AND  CENTERING. 

The  falsework  and  centering,  Fig.  56,  constitute  that  part  of  the  temporary 
wood  work  which  supports  the  concrete  while  it  is  being  laid  and  until  it  has 
hardened.  The  falsework  consists  of  vertical  timbers  braced  transversely  and 
longitudinally  upon  which  rest  the  centering  or  curved  platform  forming  the 
support  for  the  concrete  arch  ring.  The  vertical  supports  may  be  either  pile3 
driven  into  the  ground  or  river  bottom  underneath  if  the  bottom  is  soft,  or 
framed  trestle  bents  resting  on  horizontal  timbers  if  the  bottom  is  hard.  The 
piles  must  be  placed  close  enough  to  carry  the  weight  above  with  practically 
no  settlement  and  must  be  braced  with  2  by  8-inch  or  2  by  lo-inch  diagonal 
timbers  spiked  or  bolted  to  the  piles. 

Transversely  to  the  length  of  the  bridge  and  spiked  or  bolted  to  the  tops  of 
the  piles,  a  cap  must  be  set  and  upon  these  caps  rest  wooden  wedges  support- 
ing the  weight  of  the  centering  above, 

The  centering  consists  usually  of  a  set  of  caps  or  cross  timbers  resting  on 
the  wedges  above  the  pile  caps,  some  longitudinal  stringers  notched  on  and 
supported  by  the  upper  caps  and  finally  of  a  closely  laid  flooring  or  lagging  rest- 
ing on  the  stringers.  The  caps  for  the  centers  are  usually  10  by  10  inch  or  12 
by  12  inch  timbers.  The  stringers  are  of  varying  size,  depending  on  the  dis- 
tance between  piles  and  the  weight  to  be  carried.  For  arches  having  spans  up 
to  100  feet,  these  stringers  are  from  2  to  4  inches  wide  and  from  12  to  14  inches 
deep,  spaced  from  i */£  to  3  feet  apart  on  centers.  The  upper  surface  of  the 
stringers  must  be  curved  to  fit  the  curvature  of  the  under  surface  of  the  arch ; 
this  is  frequently  done  by  nailing  a  curved  piece  to  the  top  of  the  stringers  as 
in  the  centering  of  the  Concord  Arch  in  Fig.  54  and  also  in  Fig.  56.  The 
stringers  must  be  braced  to  one  another  by  i  by  6-inch  bridging  as  is  common 
in  ordinary  house  floors. 

Lagging,  consisting  of  %-mch  tongued  and  grooved  pine  or  2-inch  spruce 
with  beveled  edges,  must  be  nailed  to  the  stringers  and  must  be  planed  on  the 
top  side  to  give  a  smooth  finish  to  the  under  surface  of  the  arch  ring.  Some- 
times where  the  stringers  are  quite  far  apart  4-inch  lagging  is  used. 

PLACING  CONCRETE. 

Before  concreting  is  begun,  the  forms  for  the  foundations  and  wing  walls 
should  be  in  place  and  thoroughly  braced  and  the  steel  reinforcement  set  and 
wired  in  place.  The  forms  and  steel  for  the  spandrel  walls  and  the  arch  ring 

in 


FIG.  66.— FALSEWORK  AND  CENTERING  FOR  ARCH  WITH  SPAN  OF  40  FEET. 

112 


may  be  placed  while  the  concrete  is  being  deposited  for  the  foundations.  As 
soon  as  the  concrete  in  the  foundations  is  up  to  the  arch,  the  arch  may  be 
begun  and  laid  in  one  or  two  days. 

First,  the  arch  ring  may  be  divided  longitudinally  into  parallel  rings  or  sec- 
tions having  a  width  of  from  3  to  5  feet,  or  even  more  if  the  span  is  not  too 
large,  and  one  of  these  sections  laid  at  a  time.  This  is  generally  the  best  plan 
to  follow. 

Or,  secondly,  the  arch  ring  is  divided  into  sections  as  shown  in  Fig.  55, 
which  shows  the  Concord  Arch  being  laid  in  large,  separate  blocks  across  the 


FIG.  57.— CENTERING  FOR  ARCH  IN  PLACE. 


bridge,  having  a  width  equal  to  that  of  the  arch  ring  and  a  length  equal  to  a 
fraction  of  the  span  length. 

Whichever  of  these  methods  is  used,  care  must  be  taken  to  avoid  undue  set- 
tlement or  distortion  of  the  centers  as  the  concreting  progresses.  If  the  second 
method  of  laying  concrete  is  used,  that  is,  in  large  transverse  blocks,  the  work 
is  usually  begun  at  each  abutment  at  the  same  time,  and  if  the  centering  is  not 
well  supported  underneath  it  will  rise  at  the  crown,  due  to  the  weight  at  the 
two  ends.  To  avoid  this  the  best  way  is  to  begin  concreting  at  the  two  abut- 
ments and  as  this  work  progresses  load  the  centering  at  the  crown  temporarily, 
adjusting  this  load  if  needs  be  to  keep  the  centers  in  proper  position.  The 
loading  at  the  crown  is  frequently  done  by  laying  a  part  of  the  arch  ring  there 

"3 


after  a  part  is  laid  at  each  abutment.     Then  the  spaces  between  these  blocks 
are  filled  in. 

For  small  arches  the  entire  ring  can  be  laid  in  one  day's  work,  and  of  course 
this  should  be  done  whenever  possible. 

EARTH  FILLING. 

After  the  concrete  is  placed  in  position  and  thoroughly  hardened  and  before 
the  centers  are  removed,  the  earth  filling  should  be  added.  As  the  earth  is 
placed,  it  should  be  compacted  by  ramming  or  rolling,  and  even  if  the  centers 
are  still  in  place  it  is  better  to  deposit  the  earth  in  layers  over  the  whole  length 
of  the  span  so  that  the  arch  is  loaded  nearly  uniformly  till  the  entire  filling  is 
in  place. 

If  the  filling  is  placed  after  the  centers  are  removed,  it  is  absolutely  neces- 
sary to  place  the  earth  uniformly  over  the  span  length  and  not  pile  a  large 
weight  on  one  side  leaving  the  other  side  unloaded. 

In  case  the  finished  roadway  is  to  have  a  surface  such  as  macadam  or  con- 
crete, great  care  should  be  taken  in  compacting  the  earth  filling,  for  otherwise 
settlement  will  take  place  in  the  filling  and  the  roadway  surface  will  also  settle. 

STRIKING  CENTERS. 

By  striking  centers  is  meant  the  lowering  of  the  centers  so  that  the  arch 
becomes  self  supporting.  The  centers  are  usually  lowered  by  removing  the 
wooden  wedges  already  mentioned  under  the  head  of  Falsework  and  Center- 
ing. These  wedges,  Fig.  56,  placed  between  the  caps  of  the  falsework  and 
those  of  the  centers,  can  be  removed  by  a  sledge  hammer,  thus  lowering  the 
centers.  Care  must  be  taken  to  lower  the  centers  gradually  and  without 
jarring  the  structure  by  allowing  a  part  to  get  its  load  suddenly. 

SURFACE  FINISHING. 

In  many  structures  the  appearance  of  the  surface  of  the  finished  concrete  is 
of  no  importance,  but  most  structures,  such  as  bridges,  which  are  constantly 
exposed  to  view,  need  some  treatment  to  render  the  outer  surfaces  neat  in 
appearance.  Oftentimes  the  structure  is  such  that  proper  selection  of  good 
tongued  and  grooved  planking  smoothly  laid,  together  with  care  in  placing 
the  concrete  against  the  forms  is  all  that  is  required  to  give  a  fairly  presentable 
surface.  This  surface  is  obtained  by  simply  forcing  a  spade  down  the  side  of 
the  forms  and  pushing  back  the  stones  so  that  the  mortar  will  flow  against 
the  face  of  the  forms  and  fill  all  stone  pockets  or  voids. 

If  a  better  finish  is  desired,  good  results  can  be  obtained  by  removing  the 

114 


forms  before  the  concrete  has  set  very  hard,  generally  from  12  to  48  hours, 
depending  upon  the  cement,  weather  and  amount  of  water  used  in  mixing,  and 
after  floating  the  green  concrete  with  water  by  rubbing  the  surface  with  a  cir- 
cular motion  with  carborundum  bricks  or  with  bricks  composed  of  i  part 
"ATLAS"  Portland  Cement  to  2  parts  sand.  If  the  concrete  can  be  worked 
when  quite  green,  a  very  satisfactory  finish  can  be  obtained  by  rubbing  the 
surface  with  stiff  wire  brushes. 

When  the  surface  of  the  concre'te  has  set  so  hard  as  to  prevent  its  being 
treated  by  rubbing  with  a  brush,  it  still  may  be  surfaced  with  a  carborundum 
block,  or  an  excellent  finish  may  be  gained  by  picking  the  concrete  surface 
with  a  hand  or  pneumatic  tool  after  the  forms  are  removed.  If  further  treat- 
ment is  deemed  necessary  the  tooled  surface  may  be  washed  with  a  weak  solu- 
tion of  acid  and  then  with  an  alkali  solution  to  neutralize  the  effect  of  the  acid. 

If  a  very  smooth  surface  is  desired,  a  veneer  of  mortar  is  sometimes  placed 
between  the  main  body  of  the  concrete  and  the  forms.  This  mortar  facing  is 
usually  composed  of  i  part  "ATLAS"  Portland  Cement  to  2  or  3  parts  sand 
and  may  be  applied  in  several  ways.  Perhaps  the  cheapest  and  easiest  method 
is  to  trowel  a  layer  of  mortar  an  inch  in  thickness  against  the  face  of  the  forms 
and  immediately  deposit  the  concrete  against  it,  thus  causing  the  two  parts  to 
become  thoroughly  united.  Another  method  is  to  hold  the  concrete  away  from 
the  forms  about  i  inch  by  means  of  sheet  iron  plates  while  the  mortar  is  being 
placed  between  the  plates  and  the  forms. 

A  granolithic  finish  is  given  the  exposed  surfaces  of  bridges  in  Philadelphia 
by  applying  a  i-inch  layer  composed  of  i  part  cement  to  2  parts  sand  to  3  parts 
broken  stone  to  the  inner  surface  of  the  forms  slightly  in  advance  of  the  con- 
crete body.  After  24  or  48  hours  the  forms  on  the  faces  of  the  bridge  are 
removed  and  the  concrete  surface  is  immediately  rubbed,  using  a  wood  block 
with  sand  and  water  and  then  washing  with  clean  water. 

Plastering  on  concrete  surfaces  exposed  to  the  weather  should  be  avoided 
as  the  plaster  is  sure  to  peel  off  and  leave  the  surface  in  an  unsightly  condition 
unless  extraordinary  precautions  are  taken.  If  plastering  is  unavoidable  the 
forms  must  be  wet  instead  of  greased.  The  surface  of  the  concrete  should  be 
picked  or  bush  hammered  to  make  it  rough,  thoroughly  wet  and  then  covered 
with  a  thin  coat  of  neat  cement  paste  upon  which  the  plaster  must  be  applied 
in  as  thin  a  layer  as  possible  and  before  the  neat  cement  paste  has  set. 


COST. 

There  are  so  many  variable  items  in  bridge  building  that  to  give  accurate 
figures  regarding  costs  is  practically  impossible.  Frequently  the  cost  is  given 
for  a  bridge  based  on  a  cubic  yard  of  concrete  as  a  unit,  while  in  other  cases 

"5 


the  cost  per  horizontal  square  foot  of  roadway  surface  is  taken  as  a  unit.  In  a 
paper  read  by  Mr.  Henry  H.  Quimby  before  the  National  Association  of 
Cement  Users  in  Cleveland,  Jan.  ii-i6,  1909,  he  states  that  the  average  cost 
per  cubic  yard  of  18  concrete  bridges  recently  built  in  Philadelphia  was  $9.75, 
with  a  minimum  of  $6.50  and  a  maximum  of  $11.25  Per  cubic  yard.  Basing 
the  cost  on  a  horizontal  area  equal  to  the  clear  span  times  the  width,  he  gives 
as  an  average  cost  for  these  bridges  $6.50  per  square  foot,  with  a  range  of  from 
$3.11  to  $9.74  per  square  foot.  These  figures  include  all  the  concrete  in  the 
arches  and  abutments. 

The  cost  of  the  O'Connor  Street  reinforced  concrete  skew  arch  bridge  in 
Ottawa*,  Canada,  was  $8.02  per  cubic  yard  as  an  average  cost  for  the  total  of 
620  cubic  yards  including  some  plain  and  some  reinforced  concrete.  The  cost 
of  the  reinforced  concrete  was  $9.80  per  cubic  yard.  This  bridge  has  a  span 
of  20  feet;  a  length  of  46  feet;  thickness  at  crown  18  inches;  a  rise  of  4  feet  10 
inches. 

The  cost  of  two  concrete  arches,  one  of  so-foot  and  the  other  of  44-foot 
span,  built  by  the  Pennsylvania  State  Highway  Department  in  1907  is  given 
by  Mr.  G.  A.  Flinkt  as  $7.50  per  cubic  yard  for  the  44-foot  span  which  contains 
243  cubic  yards  of  concrete,  and  $9.50  per  cubic  yard  for  the  so-foot  span  con- 
taining 268  cubic  yards.  The  5O-foot  span  has  a  rise  of  6  feet  9  inches,  which 
is  quite  small  for  a  bridge  of  this  length. 


*The  Concrete  Review,  Vol.  3,  Nov.  i,  1908,  pf 
tGood  Roads  Magazine,  April,  1908,  p.  in. 


CHAPTER  VIII. 

RETAINING  WALLS. 

Retaining  walls  are  frequently  required  to  hold  back  an  adjoining  mass  of 
earth  from  sliding  upon  a  highway  or  for  supporting  the  lower  side  of  a  high- 
way on  a  side  hill.  In  fact,  where  the  highway  is  cut  in  the  side  of  a  hill  it 
may  be  necessary  to  use  a  retaining  wall  on  the  up-hill  as  well  as  the  down-hill 
side  of  the  road.  Walls  are  also  necessary  in  many  cases  where  an  embank- 
ment is  confined  to  a  limited  width  as,  for  instance,  where  the  highway  is 
carried  up  to  and  over  a  railroad  on  an  inclined  embankment  which  is  confined 
on  either  side  of  the  roadway  by  a  wall  running  parallel  with  the  roadway. 


FIG.  58.— RETAINING  WALLS  AT  DELLWOOD  PARK,  JOLIET,  ILL. 

Fig.  58  illustrates  a  use  of  retaining  walls  which  is  quite  common.  The 
two  walls  shown  hold  back  the  earth  on  either  side  of  an  inclined  passage  way 
leading  to  the  subway  entrance  in  Dellwood  Park,  near  Joliet,  Illinois.  In  the 
left  of  the  picture  is  a  highway  and  on  the  right  the  park.  These  walls  were 
built  of  concrete  made  of  "ATLAS"  Portland  Cement. 

Retaining  walls  are  needed  in  many  places  in  addition  to  the  uses  already 
cited. 

"7 


Concrete  retaining  walls  are  built  either  with  or  without  steel  reinforce- 
ment and  they  have  come  into  prominence  because  they  are  more  economical 
than  the  stone  masonry  walls  so  universally  used  until  a  few  years  ago.  Con- 
crete has  already  demonstrated  its  usefulness  as  a  material  for  wall  construc- 
tion, not  only  because  of  its  low  first  cost,  but  also  because  no  maintenance  is 
necessary.  A  stone  retaining  wall  must  be  pointed  from  time  to  time  to  keep 
the  joints  closed  or  the  masonry  will  soon  be  disintegrated  by  frost.  Concrete 
walls  have  practically  no  joints  and  hence  no  maintenance  charges. 


Qmff/ever  Type  Cov/jfer/brr  Type 

FIG.  59,-^TYPES  OF  REINFORCED  CONCRETE  RETAINING  WALLS 


KINDS  OF  RETAINING  WALLS. 

Retaining  walls  are  built  in  the  form  of  thin  reinforced  concrete  walls  or  as 
gravity  walls  of  plain  concrete  containing  little  or  no  steel  reinforcement. 
Gravity  walls  are  designed  to  withstand  the  earth  pressure  behind  them  by 


being  made  sufficiently  heavy  to  prevent  sliding  or  overturning.     They  do  not 
utilize  the  weight  of  the  earth  behind  them  to  add  to  their  strength. 

Reinforced  concrete  walls,  however,  depend  to  a  considerable  extent  on  the 
earth  sustained  to  add  to  their  stability.  The  earth  behind  the  walls  presses 
against  it,  but  at  the  same  time  the  wall  is  of  such  a  shape  that  this  earth  pres- 
sure helps  to  some  extent  to  prevent  sliding  or  overturning.  Reinforced  walls 
can  be  made  much  thinner  than  gravity  walls  and  for  this  reason  reinforced 
walls  are  usually  cheaper. 

Reinforced  walls  as  usually  built  consist  of  a  thin  vertical  wall  attached  to 
a  horizontal  base  and  braced  either  by  counterforts  on  the  back  or  by  but- 


RETAINING  WALLS,  BIRMINGHAM,  ALA. 

tresses  on  the  front  side.  In  more  recent  designs  no  buttresses  or  counterforts 
are  used  and  the  wall  then  is  a  vertical  slab  of  reinforced  concrete  attached  to 
a  horizontal  base. 

Fig.  59  illustrates  the  two  more  usual  types  of  reinforced  concrete  walls, 
cantilever  and  counterfort  types. 

Buttresses  projecting  out  in  front  of  the  wall  are  not  often  used,  for  they 
take  up  too  much  space  which  in  many  cases  must  be  utilized  for  other  pur- 
poses. In  addition  they  give  a  very  unsightly  appearance  to  the  face  of  the 
wall. 

Counterforts  are  thin  walls  running  back  into  the  earth  behind  and  serve  to 

119 


brace  the  main  vertical  wall.  They  are  quite  frequently  used,  but  the  inverted 
T-shaped  cantilever  type  is  so  much  more  easily  and  cheaply  constructed  that 
it  should  be  used  unless  the  wall  is  at  least  18  feet  high  above  ground,  in  which 
case  the  counterfort  type  may  be  more  economical.  Counterforts  rest  on  and 
are  connected  to  the  horizontal  base  of  the  wall,  and,  being  reinforced  with 
steel  bars,  they  really  act  as  ties  on  the  back  of  the  wall. 

GRAVITY  RETAINING  WALLS. 
With  a  gravity  type  of  construction,  the  weight  of  the  wall  is  relied  upon 


BEAM  BRIDGE  ON  PRIVATE  ESTATE,  REDLANDS,  CAL. 

to  sustain  the  earth  pressure  and  the  wall  must  not  only  be  of  sufficient  weight 
but  also  must  have  the  proper  shape. 

In  the  construction  of  retaining  walls  of  any  shape  or  kind,  care  must  be 
taken  to  get  good  foundations.  If  the  material  under  the  wall  is  compact 
sand  or  gravel,  there  should  be  no  trouble  with  the  foundation.  In  some  cases, 
where  it  is  necessary  to  build  a  wall  on  rather  soft  ground,  the  sub-soil  must  be 
thoroughly  drained  and  in  addition  it  must  be  compacted  by  ramming  sand  or 
gravel  or  stone  into  it.  Where  the  soil  is  very  soft,  piles  are  required  to  sustain 
the  weight  of  the  wall  with  the  earth  pressure  behind  it.  In  building  walls 
upon  rock  which  has  an  inclined  surface,  this  surface  must  be  made  horizontal, 
stepped,  or  roughened  by  blasting  to  prevent  the  wall  from  sliding  down  the 

120 


inclined  rock  surface.  Several  large  retaining  walls  have  failed  because  this 
was  not  regarded.  By  taking  the  precautions  just  mentioned  no  trouble  will 
be  experienced. 

Gravity  walls  are  usually  made  with  a  coping  on  top  of  the  main  body  of 
the  wall.  The  front  or  exposed  face  of  the  wall  is  sometimes  made  vertical 
and  is  sometimes  given  a  batter,  that  is  slightly  inclined,  and  the  back  side  of 
the  gravity  wall  is  either  sloped  or  stepped  so  that  the  base  of  the  wall  is 
thicker  than  the  top.  A  slight  batter  on  the  face  adds  to  the  appearance  of  the 
construction,  but  too  large  a  batter  makes  the  wall  look  as  if  it  were  leaning 
backwards.  For  low  walls,  say  those  under  12  or  15  feet  in  height,  the  face 
may  be  made  vertical,  although  a  batter  of  ^  inch  per  foot  while  not  abso- 
lutely necessary  is  desirable.  In  heavy  construction  this  batter  is  sometimes 
exceeded,  but  should  never  be  more  than  i^  inches  per  foot. 


COPINGS. 

The  coping  for  a  gravity  wall  should  overhang  the  front  surface  of  the  wall 
2  or  3  inches  and  should  be  from  12  to  18  inches  deep,  depending  on  the  height 
of  the  wall.  For  heights  of  less  than  15  feet  a  coping  12  inches  deep  should  be 
used,  while  for  walls  of  greater  heights  the  coping  should  be  15  to  18  inches 
deep. 

The  top  surface  of  the  coping  should  be  sloped  backward  so  that  dirt  will 
not  be  washed  towards  the  front  edge  of  the  coping  and  thus  will  not  drop  on 
the  front  face  of  the  wall  and  discolor  it.  The  back  edge  of  the  top  surface 
should  be  *4  inch  below  the  front  edge.  The  front  surface  of  the  coping  should 
be  vertical  and  the  back  is  sometimes,  though  not  always,  made  so.  The  two 
upper  corners  and  the  front  lower  corner  should  be  beveled  off  so  that  there 
will  be  no  sharp  corners  of  concrete  exposed.  This  beveling  can  be  best  done 
by  nailing  in  the  forms  strips  of  molding  having  triangular  cross  sections. 

Copings  may  be  laid  on  top  of  the  wall  after  the  concrete  in  the  wall  is 
hardened  or  they  may  be  laid  at  the  same  time  as  the  body  of  the  wall.  The 
top  and  front  surface  of  the  coping  to  a  depth  of  2  inches  may  be  made  of  a 
mortar  of  i  part  "ATLAS"  Portland  cement  and  2  parts  clean  sand  laid  be- 
tween the  forms  and  the  inner  body  of  the  concrete.  In  no  case  should  the 
mortar  be  plastered  on  the  concrete  after  the  latter  has  hardened.  The  upper 
surface  of  the  coping  should  be  "floated*  or  finished  in  the  same  manner  as  is 
the  wearing  surface  of  side  walls. 

Copings  should  be  laid  with  vertical  joints  to  match  the  vertical  joints  in 
the  body  o£  the  retaining  wall. 


121 


FORMS  FOR  GRAVITY  WALLS. 

In  Fig.  60  is  shown  a  good  arrangement  for  the  construction  of  forms  for  a 
gravity  wall  and  a  movable  form*  for  building  the  coping  in  sections  12  feet 
long  is  likewise  shown  in  the  same  figure. 


FIG.  60.— FORMS  FOR  GRAVITY  RETAINING  WALL 


The  forms  for  the  wall  consist  of  sheeting  made  of  i*/2  or  2-inch  lumber 
braced  by  2  by  4-inch  studs  and  2  by  4-inch  inclined  struts  spiked  to  a  post 
driven  in  the  ground.  The  front  and  back  forms  are  separated  by  means  of  2 
by  4-inch  braces  or  by  ^-inch  bolts  running  through  both  of  them  and  also 
through  a  piece  of  i  or  i^-inch  pipe  between  them,  these  pipes  serving  as 
spacers  for  the  two  forms  as  well.  Wires  are  sometimes  used  in  place  of  the 
bolts,  but  they  are  apt  to  stretch  or  break  and  bolts  are  better. 

In  placing  concrete  in  the  forms,  care  must  be  taken  to  avoid  any  longitu- 
dinal joints  on  the  front  face  of  the  wall.  To  this  end  the  wall  should  be  divided 
into  short  sections  such  that  the  work  in  one  section  can  be  completed  without 
leaving  any  horizontal  joints.  Of  course  in  such  an  arrangement  the  forms 
have  to  be  planked  up  at  the  outer  end  of  the  section,  these  end  boards  being 
removed  when  the  adjoining  section  is  begun. 


""Engineering  News/1  VoL  L.,  July  9,  1903,  p.  37. 


122 


The  movable  form  shown  in  Fig.  60  is  useful  where  the  coping  is  built  after 
the  body  of  the  wall.  These  forms  are  made  in  sections  12  feet  in  length  with 
3  of  the  bracing  frames,  one  at  each  end  and  one  in  the  middle  of  the  1 2-foot 
section.  They  are  held  in  place  on  top  of  the  wall  and  the  coping  concrete  is 
deposited  within  the  form  and  after  the  concrete  has  set  the  bolts  at  the  points 
shown  are  removed  so  that  the  forms  can  be  taken  off. 


DIMENSIONS  OF  GRAVITY  WALLS. 

The  accompanying  table  shows  dimensions  and  quantities  of  concrete  for 
gravity  walls  shown  in  Fig.  60,  with  heights  varying  from  6  feet  to  20  feet,  the 
heights  being  the  difference  in  elevation  between  the  upper  and  lower  levels  of 
the  earth. 


DIMENSIONS  AND  QUANTITIES  OF  GRAVITY  RETAINING  WALLS 


Height 
Above  Ground 
Level, 
Feet 

Width  of  Base 

Total  Height         Batter  on  Face 
Feet                        Inches 

Cubic  Yds    Con- 
crete   in    Wall 
1  Foot  Lonj 

6 

2  ft       3  in. 

10                            4  y> 

064 

8 

3 

0 

12                    &y; 

0,92 

10 

3 

9 

14                    &y2 

1.26 

12 

4 

6 

16                            7  Yz 

1.65 

14 

5 

3 

is                   &y2 

2.10 

16 

6 

0 

20                            9^ 

2.61 

18 

6 

9 

22                          10  y. 

317 

20 

7 

6 

21                    11  y> 

3.78 

The  bottom  of  the  wall  should  in  all  cases  go  well  below  the  frost  line 
Four  feet  has  been  taken  in  this  case,  though  of  course  this  will  vary  with  dif- 
ferent localities.  Four  feet,  however,  is  usually  enough,  even  in  the  coldest 
climates.  The  coping  is  shown  12  inches  high  and  18  inches  wide  on  top  and 
the  top  surface  should  have  at  least  a  ^4-inch  slope  towards  the  back. 

The  width  of  the  base  must  of  course  be  made  larger  as  the  height  of  the 
wall  increases.  For  highway  work  where  the  upper  surface  of  the  ground  is 
horizontal  and  level  with  the  top  of  the  wall  it  is  customary  to  make  the  base 
y%  of  the  height  of  the  wall,  the  height  being  taken  as  the  distance  between  the 
upper  and  lower  levels  of  the  ground,  thus :  if  the  height  of  the  wall  is  20  feet 
the  base  would  be  %  of  20,  that  is  7^2  feet.  The  batter  on  the  front  face  is  y2 
inch  per  foot  of  vertical  distance  under  the  coping,  that  is,  y2  times  23  or  n1/^ 
inches.  In  this  case  the  amount  in  i  foot  length  of  wall  is  3.78  cubic  yards. 


123 


Where  the  earth  to  be  sustained  is  rather  wet  and  slopes  up  from  the  top  of 
the  wall  instead  of  being  horizontal,  the  thickness  of  the  base  should  be  */£  of 
the  height  of  the  wall. 


FIG.  81.— SECTIONS  FOR  REINFORCED  RETAINING  WALLS. 

REINFORCED  RETAINING  WALLS. 

The  cantilever  retaining  walls  shown  in  Fig.  61  consist  of  a  vertical  slab 
of  reinforced  concrete  attached  to  a  reinforced  concrete  base,  the  whole  sec- 
tion being  really  an  inverted  T.  The  figure  shows  designs  for  2  walls,  one 
for  a  total  height  of  8  feet,  the  other  12  feet.  In  severe  climates  the  bottom 
of  these  walls  should  be  placed  4  feet  below  the  surface  of  the  ground  in  front 
of  them,  thus  making  the  visible  height  of  the  finished  wall  4  feet  and  6  feet 
respectively.  Maximum  pressure  on  soil  from  these  walls  is  2  tons  per  sq.  ft. 


124 


Great  care  must  be  taken  to  place  the  steel  reinforcement  in  the  exact 
positions  called  for  by  the  drawing.  In  each  wall  the  reinforcement  consists 
of  5  sets  of  reinforcing  bars.  In  the  base  of  the  1 2-foot  wall  there  is  one  set 
of  horizontal  half-inch  round  bars  spaced  4  inches  apart  and  i^  inches  above 
the  lower  edge  of  the  base.  Near  the  upper  surface  of  the  base  there  is  a  set 
of  54-inch  round  rods  spaced  4%  inches  apart  and  slightly  inclined  as  shown 
in  the  drawing.  In  the  vertical  parts  of  the  wall  there  are  two  sets  of  5/s-inch 
round  horizontal  rods,  one  set  near  the  front  face  and  one  near  the  rear  face  of 
the  wall.  Also  in  the  vertical  part  there  is  a  set  of  54-inch  round  vertical  rods 


ARCH  IN  PHILLIPS  PARK,  AURORA,  ILL: 


near  the  back  of  the  wall.  These  vertical  rods  must  be  imbedded  in  the  base 
as  shown.  In  this  set  of  vertical  rods  every  fifth  rod  should  extend  from  the 
bottom  to  the  top  of  the  wall,  these  rods  being  17  inches  apart.  Then  midway 
between  each  pair  of  these  long  rods  a  shorter  rod  extends  from  the  bottom  of 
the  wall  2/3  of  the  way  to  the  top,  making  the  rods  in  the  middle  third  of  the 
height  S%  inches  apart.  In  the  lower  third  of  the  height  there  are  in  addi- 
tion to  the  rods  mentioned  short  rods  running  from  the  base  up  1/3  of  the 
height  of  the  wall,  thus  making  the  rods  in  this  lower  third  4%  inches  c.  to  c. 
Although  54-inch  round  rods  are  shown  in  the  figure,  other  bars  having 
the  same  cross  sectional  area  can  be  used  instead. 

125 


PROPORTIONS  OF  CONCRETE. 

For  gravity  walls  similar  to  those  described  in  this  chapter  for  the  body  of 
the  wall  and  for  the  body  of  the  coping  the  concrete  should  be  mixed  i  part 
"ATLAS*  Portland  Cement,  3  parts  sand  and  6  parts  broken  stone  or  gravel. 
For  the  upper  and  front  surfaces  of  the  coping  a  2-inch  veneer  of  mortar 
mixed  i  part  "ATLAS"  Portland  Cement  and  2  parts  sand  may  be  used,  built 
on  a  part  of  the  coping  at  the  same  time  that  the  concrete  is  placed.  For  a 
gravity  wall  having  a  height  of  more  than  12  feet  "one-man"  stones  may  be 


BEAM  BRIDGE,  SUDBURY,  MASS. 

imbedded  in  the  concrete  as  indicated  in  Chapter  I  under  the  head  of  Rubble 
Concrete. 

For  reinforced  concrete  walls  similar  to  those  described  in  this  chapter 
concrete  should  be  mixed  i  part  "ATLAS"  Portland  Cement,  2*4  parts  sand 
and  5  parts  broken  stone  or  gravel. 

In  depositing  the  concrete  against  the  forms,  care  must  be  taken  to  pre- 
vent the  larger  stones  from  collecting  in  pockets  against  the  forms  and  thus 
making  voids  which  will  show  when  the  forms  are  removed. 

136 


EXPANSION  JOINTS. 

When  concrete  is  subjected  to  changes  in  temperature  it  will  expand  or 
contract.  Therefore,  in  long  retaining  walls  vertical  cracks  will  form  in  the 
concrete  unless  the  wall  is  either  reinforced  with  steel  or  vertical  joints  are 
made  at  frequent  intervals.  For  plain  concrete  walls  vertical  joints  should 
be  left  at  intervals  not  exceeding  30  feet;  these  joints  allowing  the  sections  of 
concrete  to  expand  or  contract  without  forming  unsightly  cracks  in  the  face 
of  the  wall.  While  30  feet  is  the  maximum  distance  between  expansion  joints 
in  plain  concrete  walls,  20  feet  is  the  proper  distance,  and  walls  provided  with 
joints  20  feet  apart  will  not  crack.  Frequently  these  joints  are  run  straight 
through  the  wall  from  front  to  back.  It  is  better,  however,  to  have  the  two 
adjacent  sections  of  the  wall  tongued-and-grooved  or  V-shaped  in  plan. 

DRAINAGE. 

Unless  provision  is  made  for  removing  the  water,  it  will  in  most  cases  collect 
behind  the  retaining  wall  and  considerably  increase  the  pressure  on  the  back 
of  the  wall.  With  clayey  soils  or  other  material  of  similar  nature,  some  pro- 
vision must  be  made  for  removing  this  water  by  drainage.  If  the  wall  is 
short,  a  broken  stone  drain  laid  lengthwise  behind  the  wall  and  properly 
graded  so  that  the  water  will  flow  along  the  back  and  then  away  from  the 
wall  will  serve  every  purpose.  In  the  case  of  long  walls,  drainage  holes  must 
be  placed  through  the  wall  so  that  the  water  may  pass  from  the  back  to  the 
front  where  it  can  be  drained  off.  These  drainage  holes  can  be  made  by  plac- 
ing cement  or  clay  tile  pipes  3  or  4  inches  in  diameter  in  the  concrete,  sloping 
downward  toward  the  front  of  the  wall.  Wooden  forms  of  i-inch  planks 
can  be  used  to  make  a  square  hole,  but  the  planks  are  hard  to  remove  after 
concreting.  The  outlet  in  the  front  face  should  be  6  inches  above  the  surface 
of  the  ground  in  front  of  the  wall.  Two  or  three  barrow  loads  of  cobble 
stones  and  gravel  should  be  placed  at  the  upper  end  where  the  pipe  pierces 
the  back  surface  of  the  wall. 

In  very  wet  soils  loose  stones  10  to  15  inches  in  thickness  should  be  piled 
up  against  the  back  of  the  wall  from  the  bottom  to  within  2  feet  of  the  top. 
This  arrangement  together  with  the  weep  holes  just  described  will  afford  per- 
fect drainage  even  in  very  wet  material. 

Weep  holes  should  be  placed  from  10  to  20  feet  apart  lengthwise  of  the 
wall,  depending  on  the  nature  of  the  soil.  They  should  be  placed  10  feet  apart 
in  wet  ground. 


127 


CHAPTER  IX. 
MISCELLANEOUS. 

FENCE  POSTS. 

Reinforced  concrete  fence  posts  are  better  than  wooden  ones  because  they 
will  not  decay,  are  more  uniform  in  size  and  shape,  and  in  the  long  run  are 
cheaper.  Fence  posts  of  wood  are  cheaper  in  first  cost  than  those  made  of 
concrete,  but  ordinary  wooden  posts  decay  in  a  comparatively  short  time 
while  concrete  construction  lasts  indefinitely.  Cast  iron  posts  last  very  well, 
but  their  cost  prohibits  their  use  except  in  a  few  cases.  Concrete  posts  prop- 
erly reinforced  with  steel  rods  possess  the  necessary  strength  and  durability 
and  at  the  same  time  may  be  obtained  in  any  locality  at  a  reasonable  cost. 


FIG.  62.— FORMS  FOR  CONCRETE  FENCE  POSTS. 

Fence  posts  for  farms  and  for  division  fences  in  city  suburbs  should  gen- 
erally be  7  feet  long,  6  inches  square  at  the  lower  and  4  inches  square  at  the 
upper  end.  These  posts  are  usually  made  to  support  wire  fences. 

For  fences  adjoining  streets  in  towns  the  posts  should  be  from  5  to  6  feet 
in  length  with  ends  the  same  size  as  for  farm  posts.  These  posts  carry  wire 

128 


fences  or  wooden  fences.  If  a  wooden  fence  is  supported  by  concrete  posts 
the  street  side  of  the  posts  should  be  set  vertical,  the  lower  wooden  stringer 
of  the  fence  being  bolted  to  the  front  vertical  face  of  the  post  and  the  upper 
stringer  bolted  on  top  of  the  post. 

A  form  for  making  an  individual  post  is  shown  in  Fig.  62  and  consists  of 
a  base  board  iy2  inches  thick  and  12  inches  wide.  Upon  this  are  set  two  bev- 
eled pieces  of  2-inch  lumber  6  inches  wide  at  one  end  and  4  inches  wide  at  the 
other.  The  two  side  boards,  connected  with  2  or  3  cross  braces  on  top,  are  set 
against,  but  not  nailed  to,  the  two  small  strips,  the  latter  being  nailed  to  the 
base  board.  The  blocks  at  the  ends  are  nailed  in  place. 


FIG.  63.— MULTIPLE  FORM  FOR  CONCRETE  FENCE  POSTS. 


Short  pieces  of  */2-inch  greased  round  rods  should  be  placed  through  the 
side  boards  before  the  concrete  is  placed  in  the  forms  and  allowed  to  remain 
four  or  five  hours  till  the  concrete  is  hardened  enough  so  that  they  can  be 
pulled  out.  The  fence  wires  can  be  run  through  these  holes  or  can  be  run  in 
front  of  the  post  and  tied  to  the  same  with  No.  12  or  14  galvanized  wire. 
These  holes  for  fence  wires  do  not  decrease  the  strength  of  the  post  and  afford 
a  better  method  of  attachment  than  staples  placed  in  the  front  surface  of  the 
post.  If  staples  are  used  they  must  be  galvanized. 

129 


With  the  form  in  place,  concrete,  made  one  part  "ATLAS"  Portland 
Cement,  two  parts  clean  coarse  sand,  and  four  parts  broken  stone  or  screened 
gravel  of  about  one  inch  diameter  particles,  should  be  placed  in  the  form  and 
tamped  to  a  thickness  of  one  inch.  Then  two  pieces  of  wire  about  3/16  inch 
in  diameter  and  6*/2  feet  long  are  placed  on  the  layer  of  concrete,  each  one  inch 
from  the  side  forms.  Another  layer  of  concrete  must  then  be  tamped  on  the 
first  layer  until  the  concrete  is  within  one  inch  of  the  top  edge  of  the  side 
forms  and  two  more  wires  like  the  first  ones  then  laid  and  the  forms  filled 
with  concrete.  After  the  concrete  is  tamped  and  smoothed  oft7  on  the  upper 
surface,  the  post  is  set  aside  and  allowed  to  lie  ten  or  twelve  hours  before  the 
side  forms  are  removed.  The  base  board  must  be  left  in  place  ten  days 
during  which  time  the  post  must  be  sprinkled  daily  and  must  not  be  disturbed. 
After  this  time  the  posts  should  be  allowed  to  harden  for  four  weeks  more 
before  being  used. 

Fig.  63  shows  a  mold  for  casting  four  posts  at  a  time.  The  boards  sep- 
arating the  posts  are  slipped  in  between  cleats  at  each  end  and  are  either 
screwed  to  the  end  pieces  or  held  in  place  by  tightening  up  the  wedges  at 
the  ends.  Wedges  bearing  against  blocks  nailed  to  the  base  board  prevent 
the  side  boards  from  spreading.  Staples  pressed  in  the  upper  face  of  the  con- 
crete before  the  concrete  sets  afford  an  easy  connection  for  the  fence  wires. 

Forms  should  be  made  of  dressed  lumber  and  should  be  oiled  or  greased 
with  soft  soap  before  using. 

Fence  posts  such  as  here  described  should  cost  from  thirty  to  fifty  cents 
each. 

Corner  posts  must  be  larger  than  the  side  posts,  10  by  10  inches  at  the 
base  and  10  by  10  inches  at  the  top,  and  9  feet  long  being  good  dimensions. 
Use  four  3^-inch  round  rods  for  reinforcement  of  3/1 6-inch. 

CONCRETE  FENCE  POSTS  AT  DELLWOOD  PARK. 

In  Fig.  64  are  shown  some  concrete  fence  posts  around  Dellwood  Park, 
four  miles  from  Joliet,  111.  This  fence*  encloses  a  tract  of  land  approximately 
1,320  feet  wide  by  2,200  feet  long  and  has  1,500  concrete  posts  varying  in 
length  from  7  to  9  feet.  At  the  top  the  posts  are  4  inches  square  and  at  the 
bottom  they  are  4  by  6  inches  in  cross  section.  The  concrete  was  made  one 
part  "ATLAS"  Portland  Cement  and  one  part  stone  screenings  passing  a 
54-inch  screen.  The  reinforcement  consists  of  four  rods,  one  in  each  corner. 

The  forms  used  were  similar  to  the  single  form  shown  in  Fig.  62  and  were 
left  on  the  posts  twenty-four  hours,  the  side  boards  being  removed  after  this 
period.  The  posts  were  then  left  for  an  additional  twenty-four  hours  lying 

*Engineering  Record,  Vol.  55,  March  23,  1907,  page  377. 

130 


on  the  base  boards  after  which  the  bases  together  with  the  post  were  moved 
to  a  platform  where  they  remained  a  week.  They  were  then  laid  out  to 
harden  till  used,  being  kept  wet  for  the  first  three  weeks  after  they  were 
made.  Two  men,  each  paid  $2  per  day,  could  make  about  forty  posts  in 
one  day.  The  cement  cost  $2  per  barrel,  the  reinforcement  3^2  cents  per 
pound  and  the  screenings  75  cents  per  cubic  yard.  The  posts,  9  feet  long, 
cost  65  cents  each,  a  rather  high  cost  because  of  the  design  and  the  richness 
of  the  proportions.  Posts  at  angles  of  the  fence  were  heavier  than  the  others 
and  were  braced. 


FIG.  64.— CONCRETE  POSTS  AT  DELLWOOD  PARK,  JOLIET,  ILL. 


HITCHING   POSTS. 

Concrete  hitching  posts  without  reinforcement  do  not  have  sufficient 
strength.  They  must  be  reinforced  with  a  3^-inch  diameter  rod  imbedded  in 
each  corner.  Hitching  posts  should  be  set  at  least  2^2  feet  in  the  ground  if 
they  are  surrounded  by  a  concrete  sidewalk.  If  set  in  earth  without  the 
surrounding  walk  they  should  be  placed  3  feet  in  the  ground.  The  outer 
surface  must  be  at  least  6  inches,  or  still  better,  8  inches  from  the  edge  of  the 
curb. 

Posts  similar  to  that  shown  at  the  left  side  of  Fig.  65  are  made  in  the  same 


manner  as  fence  posts  except  that  there  is  a  2-inch  ring  attached  to  a  staple  in 
the  top. 

The  post  shown  in  the  right  half  of  Fig.  65  is  neat  but  is  more  difficult  to 
make  than  the  plain  post.  The  depressed  surfaces  on  the  sides  are  one-half 
inch  deep  and  are  best  formed  by  nailing  one-half-inch  wooden  pieces  to  the 
inside  of  the  forms.  Tamp  the  concrete  into  the  corners  of  the  molds  well 
and  after  the  forms  are  removed  give  the  surfaces  of  the  posts  a  coating  of 
cement  mixed  with  water,  applied  with  a  brush. 


/        /o  3/&p/e 


//?  eac/?  ca/7?er      /-< 

FIG.  65.— CONCRETE  HITCHING  POSTS. 


LAMP  POSTS. 

Concrete  is  being  used  for  lamp  posts  to  support  electric  lights  in  parks 
and  other  similar  places.  These  posts  are  usually  about  20  to  24  feet  in 
length  and  are  set  5  or  6  feet  into  the  ground.  They  should  be  6  or  8  inches 
in  diameter  at  the  bottom  and  4  or  5  inches  at  the  top,  the  larger  diameters 
being  required  for  the  highest  posts.  A  piece  of  i-inch  gas  pipe  is  placed  in 
the  center  of  the  post  throughout  its  length  to  carry  the  wires  from  the  lamp 
to  the  bottom  of  the  post  where  the  wires  then  connect  with  the  underground 

132 


electric  system.  The  lamp  can  be  set  directly  on  top  of  the  post  or  it  can  be 
suspended  from  the  outer  end  of  a  curved  pipe  which  is  connected  to  the  pipe 
passing  down  through  the  post.  The  methods  of  construction  are  similar  to 
those  used  in  making  fence  posts. 

One  rod  one-half  inch  in  diameter  in  each  corner  of  a  square  post  is  suffi- 
cient for  reinforcement.  A  square  post  with  beveled  edges  is  simpler  to  make 
than  a  round  post,  but  is  not  quite  so  neat  in  appearance. 


BRIDGE  AND  DRINKING  FOUNTAIN,  LINCOLN  PARK,  CHICAGO,  ILL 


DRINKING   FOUNTAINS. 

Drinking  fountains  of  concrete  are  giving  good  satisfaction  in  parks  even 
where  the  climate  is  severe.  These  fountains  are  generally  made  with  a 
circular  base  about  3  feet  in  diameter  and  a  circular  stem  and  bowl  on  top; 
the  stem  gradually  diminishing  in  diameter  from  the  base  and  then  enlarging 
into  the  bowl  which  is  from  3^/2  to  4  feet  in  diameter. 

Reinforcement  must  be  used  in  fountains  to  give  them  sufficient  strength 
to  withstand  shocks.  Wire  mesh  of  any  kind  bent  to  shape  and  imbedded  in 
the  concrete  is  all  that  is  necessary. 

The  concrete  must  be  mixed  quite  wet,  about  ^the  consistency  of  thick 
cream  and  in  the  proportions  of  i  part  "ATLAS"  Portland  Cement,  i*4  parts 


clean,  coarse  sand,  and  3  parts  broken  stone  or  screened  gravel  of  about  i  inch 
diameter. 

The  bowl  must  be  cast  at  one  operation  and  as  quickly  as  possible  so  that 
it  will  be  water  tight. 

Good  drinking  fountains  of  this  kind  have  been  built  for  $12  with  $5  for 
the  setting. 


BRIDGE  WITH  OPEN  SPANDRELS,  CHICAGO,  ILL. 


134 


BRIDGE  AT  HAWORTH,  N.  J. 


PARKWAY  BRIDGE.  MEDFORD,  MASS. 
135 


136 


Ask  Your  Dealer  for  Price  on 
" Atlas '  -If  he  cannot  supply  you 
write  to 

The  Atlas  Portland  Cement  Go.f 
30  Broad  Street, 

New  York  City. 


bought  by  the  Unite 
States  Government  fl 
™e  Panama  Canal. 

^^^••••BdiMaMIBteHBbA.  ~««M»,,.  .,£,,     ., 


MAKERS 

SYRACUSE,  -  N.Y. 


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26  1934 
1934 


LD  2 1-100) 


